diff --git a/bind/benchmark/benchmark.go b/bind/benchmark/benchmark.go
index 1d81ab7..2e56861 100644
--- a/bind/benchmark/benchmark.go
+++ b/bind/benchmark/benchmark.go
@@ -29,6 +29,8 @@ type Benchmarks interface {
 	Ref(_ I)
 	Manyargs(_, _, _, _, _, _, _, _, _, _ int)
 	String(_ string)
+	StringRetShort() string
+	StringRetLong() string
 	Slice(_ []byte)
 }
 
@@ -94,6 +96,8 @@ func RunBenchmarks(b Benchmarks) {
 		"StringLong",
 		"StringShortUnicode",
 		"StringLongUnicode",
+		"StringRetShort",
+		"StringRetLong",
 		"SliceShort",
 		"SliceLong",
 	}
@@ -118,6 +122,8 @@ func RunBenchmarks(b Benchmarks) {
 	runGoBenchmark("StringLong", func() { b.String(LongString) })
 	runGoBenchmark("StringShortUnicode", func() { b.String(ShortStringUnicode) })
 	runGoBenchmark("StringLongUnicode", func() { b.String(LongStringUnicode) })
+	runGoBenchmark("StringRetShort", func() { b.StringRetShort() })
+	runGoBenchmark("StringRetLong", func() { b.StringRetLong() })
 	runGoBenchmark("SliceShort", func() { b.Slice(ShortSlice) })
 	runGoBenchmark("SliceLong", func() { b.Slice(LongSlice) })
 }
@@ -138,6 +144,14 @@ func Oneret() int {
 func String(_ string) {
 }
 
+func StringRetShort() string {
+	return ShortString
+}
+
+func StringRetLong() string {
+	return LongString
+}
+
 func Slice(_ []byte) {
 }
 
diff --git a/bind/gen.go b/bind/gen.go
index aac6842..6bd2e01 100644
--- a/bind/gen.go
+++ b/bind/gen.go
@@ -30,26 +30,15 @@ type (
 const (
 	// modeTransient are for function arguments that
 	// are not used after the function returns.
-	// Transient strings and byte slices don't need copying
+	// Transient byte slices don't need copying
 	// when passed accross the language barrier.
 	modeTransient varMode = iota
-	// modeRetained are for function arguments that are
-	// used after the function returns. Retained strings
-	// don't need an intermediate copy, while byte slices do.
+	// modeRetained are for returned values and for function
+	// arguments that are used after the function returns.
+	// Retained byte slices need an intermediate copy.
 	modeRetained
-	// modeReturned are for values that are returned to the
-	// caller of a function. Returned values are always copied.
-	modeReturned
 )
 
-func (m varMode) copyString() bool {
-	return m == modeReturned
-}
-
-func (m varMode) copySlice() bool {
-	return m == modeReturned || m == modeRetained
-}
-
 func (list ErrorList) Error() string {
 	buf := new(bytes.Buffer)
 	for i, err := range list {
diff --git a/bind/gengo.go b/bind/gengo.go
index 5a85e92..805b559 100644
--- a/bind/gengo.go
+++ b/bind/gengo.go
@@ -76,7 +76,7 @@ func (g *goGen) genFuncBody(o *types.Func, selectorLHS string) {
 
 	for i := 0; i < res.Len(); i++ {
 		pn := fmt.Sprintf("res_%d", i)
-		g.genWrite("_"+pn, pn, res.At(i).Type(), modeReturned)
+		g.genWrite("_"+pn, pn, res.At(i).Type(), modeRetained)
 	}
 	if res.Len() > 0 {
 		g.Printf("return ")
@@ -105,7 +105,7 @@ func (g *goGen) genWrite(toVar, fromVar string, t types.Type, mode varMode) {
 	case *types.Basic:
 		switch t.Kind() {
 		case types.String:
-			g.Printf("%s := encodeString(%s, %v)\n", toVar, fromVar, mode.copyString())
+			g.Printf("%s := encodeString(%s)\n", toVar, fromVar)
 		case types.Bool:
 			g.Printf("var %s C.%s = 0\n", toVar, g.cgoType(t))
 			g.Printf("if %s { %s = 1 }\n", fromVar, toVar)
@@ -117,7 +117,7 @@ func (g *goGen) genWrite(toVar, fromVar string, t types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("%s := fromSlice(%s, %v)\n", toVar, fromVar, mode.copySlice())
+				g.Printf("%s := fromSlice(%s, %v)\n", toVar, fromVar, mode == modeRetained)
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
@@ -219,7 +219,7 @@ func (g *goGen) genStruct(obj *types.TypeName, T *types.Struct) {
 		g.Indent()
 		g.Printf("ref := _seq.FromRefNum(int32(refnum))\n")
 		g.Printf("v := ref.Get().(*%s.%s).%s\n", g.pkg.Name(), obj.Name(), f.Name())
-		g.genWrite("_v", "v", f.Type(), modeReturned)
+		g.genWrite("_v", "v", f.Type(), modeRetained)
 		g.Printf("return _v\n")
 		g.Outdent()
 		g.Printf("}\n\n")
@@ -257,7 +257,7 @@ func (g *goGen) genVar(o *types.Var) {
 	g.Printf("func var_get%s_%s() C.%s {\n", g.pkgPrefix, o.Name(), g.cgoType(o.Type()))
 	g.Indent()
 	g.Printf("v := %s\n", v)
-	g.genWrite("_v", "v", o.Type(), modeReturned)
+	g.genWrite("_v", "v", o.Type(), modeRetained)
 	g.Printf("return _v\n")
 	g.Outdent()
 	g.Printf("}\n")
@@ -333,13 +333,13 @@ func (g *goGen) genInterface(obj *types.TypeName) {
 		if res.Len() > 0 {
 			if res.Len() == 1 {
 				T := res.At(0).Type()
-				g.genRead("_res", "res", T, modeReturned)
+				g.genRead("_res", "res", T, modeRetained)
 				retName = "_res"
 			} else {
 				var rvs []string
 				for i := 0; i < res.Len(); i++ {
 					rv := fmt.Sprintf("res_%d", i)
-					g.genRead(rv, fmt.Sprintf("res.r%d", i), res.At(i).Type(), modeReturned)
+					g.genRead(rv, fmt.Sprintf("res.r%d", i), res.At(i).Type(), modeRetained)
 					rvs = append(rvs, rv)
 				}
 				retName = strings.Join(rvs, ", ")
@@ -361,7 +361,7 @@ func (g *goGen) genRead(toVar, fromVar string, typ types.Type, mode varMode) {
 	case *types.Basic:
 		switch t.Kind() {
 		case types.String:
-			g.Printf("%s := decodeString(%s, %v)\n", toVar, fromVar, mode.copyString())
+			g.Printf("%s := decodeString(%s)\n", toVar, fromVar)
 		case types.Bool:
 			g.Printf("%s := %s != 0\n", toVar, fromVar)
 		default:
@@ -372,7 +372,7 @@ func (g *goGen) genRead(toVar, fromVar string, typ types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("%s := toSlice(%s, %v)\n", toVar, fromVar, mode.copySlice())
+				g.Printf("%s := toSlice(%s, %v)\n", toVar, fromVar, mode == modeRetained)
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
diff --git a/bind/genjava.go b/bind/genjava.go
index ffdba86..3749bc2 100644
--- a/bind/genjava.go
+++ b/bind/genjava.go
@@ -404,7 +404,7 @@ func (g *javaGen) genJavaToC(varName string, t types.Type, mode varMode) {
 	case *types.Basic:
 		switch t.Kind() {
 		case types.String:
-			g.Printf("nstring _%s = go_seq_from_java_string(env, %s, %d);\n", varName, varName, g.toCFlag(mode.copyString()))
+			g.Printf("nstring _%s = go_seq_from_java_string(env, %s);\n", varName, varName)
 		default:
 			g.Printf("%s _%s = (%s)%s;\n", g.cgoType(t), varName, g.cgoType(t), varName)
 		}
@@ -413,7 +413,7 @@ func (g *javaGen) genJavaToC(varName string, t types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("nbyteslice _%s = go_seq_from_java_bytearray(env, %s, %d);\n", varName, varName, g.toCFlag(mode.copySlice()))
+				g.Printf("nbyteslice _%s = go_seq_from_java_bytearray(env, %s, %d);\n", varName, varName, g.toCFlag(mode == modeRetained))
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
@@ -454,7 +454,7 @@ func (g *javaGen) genCToJava(toName, fromName string, t types.Type, mode varMode
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("jbyteArray %s = go_seq_to_java_bytearray(env, %s, %d);\n", toName, fromName, g.toCFlag(mode.copySlice()))
+				g.Printf("jbyteArray %s = go_seq_to_java_bytearray(env, %s, %d);\n", toName, fromName, g.toCFlag(mode == modeRetained))
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
@@ -579,7 +579,7 @@ func (g *javaGen) genJNIField(o *types.TypeName, f *types.Var) {
 	g.Printf("int32_t o = go_seq_to_refnum(env, this);\n")
 	g.Printf("%s r0 = ", g.cgoType(f.Type()))
 	g.Printf("proxy%s_%s_%s_Get(o);\n", g.pkgPrefix, o.Name(), f.Name())
-	g.genCToJava("_r0", "r0", f.Type(), modeReturned)
+	g.genCToJava("_r0", "r0", f.Type(), modeRetained)
 	g.Printf("return _r0;\n")
 	g.Outdent()
 	g.Printf("}\n\n")
@@ -602,7 +602,7 @@ func (g *javaGen) genJNIVar(o *types.Var) {
 	g.Indent()
 	g.Printf("%s r0 = ", g.cgoType(o.Type()))
 	g.Printf("var_get%s_%s();\n", g.pkgPrefix, o.Name())
-	g.genCToJava("_r0", "r0", o.Type(), modeReturned)
+	g.genCToJava("_r0", "r0", o.Type(), modeRetained)
 	g.Printf("return _r0;\n")
 	g.Outdent()
 	g.Printf("}\n\n")
@@ -650,7 +650,7 @@ func (g *javaGen) genJNIFunc(o *types.Func, sName string, proxy bool) {
 	for i := 0; i < res.Len(); i++ {
 		tn := fmt.Sprintf("_r%d", i)
 		t := res.At(i).Type()
-		g.genCToJava(tn, fmt.Sprintf("%sr%d", resPrefix, i), t, modeReturned)
+		g.genCToJava(tn, fmt.Sprintf("%sr%d", resPrefix, i), t, modeRetained)
 	}
 	// Go backwards so that any exception is thrown before
 	// the return.
@@ -674,20 +674,12 @@ func (g *javaGen) genRelease(varName string, t types.Type, mode varMode) {
 	}
 	switch t := t.(type) {
 	case *types.Basic:
-		switch t.Kind() {
-		case types.String:
-			if !mode.copyString() {
-				g.Printf("if (_%s.chars != NULL) {\n", varName)
-				g.Printf("  (*env)->ReleaseStringChars(env, %s, _%s.chars);\n", varName, varName)
-				g.Printf("}\n")
-			}
-		}
 	case *types.Slice:
 		switch e := t.Elem().(type) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				if !mode.copySlice() {
+				if mode == modeTransient {
 					g.Printf("if (_%s.ptr != NULL) {\n", varName)
 					g.Printf("  (*env)->ReleaseByteArrayElements(env, %s, _%s.ptr, 0);\n", varName, varName)
 					g.Printf("}\n")
@@ -727,14 +719,14 @@ func (g *javaGen) genMethodInterfaceProxy(oName string, m *types.Func) {
 		var rets []string
 		t := res.At(0).Type()
 		if !isErrorType(t) {
-			g.genJavaToC("res", t, modeReturned)
+			g.genJavaToC("res", t, modeRetained)
 			retName = "_res"
 			rets = append(rets, retName)
 		}
 		if res.Len() == 2 || isErrorType(t) {
 			g.Printf("jstring exc = go_seq_get_exception_message(env);\n")
 			st := types.Typ[types.String]
-			g.genJavaToC("exc", st, modeReturned)
+			g.genJavaToC("exc", st, modeRetained)
 			retName = "_exc"
 			rets = append(rets, "_exc")
 		}
diff --git a/bind/genobjc.go b/bind/genobjc.go
index 509c626..c047e0c 100644
--- a/bind/genobjc.go
+++ b/bind/genobjc.go
@@ -257,7 +257,7 @@ func (g *objcGen) genVarM(o *types.Var) {
 	g.Indent()
 	g.Printf("%s r0 = ", g.cgoType(o.Type()))
 	g.Printf("var_get%s_%s();\n", g.pkgPrefix, o.Name())
-	g.genRead("_r0", "r0", o.Type(), modeReturned)
+	g.genRead("_r0", "r0", o.Type(), modeRetained)
 	g.Printf("return _r0;\n")
 	g.Outdent()
 	g.Printf("}\n\n")
@@ -470,7 +470,7 @@ func (g *objcGen) genGetter(oName string, f *types.Var) {
 	g.Printf("int32_t refnum = go_seq_go_to_refnum(self._ref);\n")
 	g.Printf("%s r0 = ", g.cgoType(f.Type()))
 	g.Printf("proxy%s_%s_%s_Get(refnum);\n", g.pkgPrefix, oName, f.Name())
-	g.genRead("_r0", "r0", f.Type(), modeReturned)
+	g.genRead("_r0", "r0", f.Type(), modeRetained)
 	g.Printf("return _r0;\n")
 	g.Outdent()
 	g.Printf("}\n\n")
@@ -510,7 +510,7 @@ func (g *objcGen) genWrite(varName string, t types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("nbyteslice _%s = go_seq_from_objc_bytearray(%s, %d);\n", varName, varName, g.toCFlag(mode.copySlice()))
+				g.Printf("nbyteslice _%s = go_seq_from_objc_bytearray(%s, %d);\n", varName, varName, g.toCFlag(mode == modeRetained))
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
@@ -577,7 +577,7 @@ func (g *objcGen) genRead(toName, fromName string, t types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				g.Printf("NSData *%s = go_seq_to_objc_bytearray(%s, %d);\n", toName, fromName, g.toCFlag(mode.copySlice()))
+				g.Printf("NSData *%s = go_seq_to_objc_bytearray(%s, %d);\n", toName, fromName, g.toCFlag(mode == modeRetained))
 			default:
 				g.errorf("unsupported type: %s", t)
 			}
@@ -635,7 +635,7 @@ func (g *objcGen) genFunc(s *funcSummary, objName string) {
 	}
 
 	for i, r := range s.retParams {
-		g.genRead("_"+r.name, fmt.Sprintf("%sr%d", resPrefix, i), r.typ, modeReturned)
+		g.genRead("_"+r.name, fmt.Sprintf("%sr%d", resPrefix, i), r.typ, modeRetained)
 	}
 
 	if !s.returnsVal() {
@@ -754,7 +754,7 @@ func (g *objcGen) genInterfaceMethodProxy(obj *types.TypeName, m *types.Func) {
 	if len(s.retParams) > 0 {
 		if s.returnsVal() { // len(s.retParams) == 1 && s.retParams[0] != error
 			p := s.retParams[0]
-			g.genWrite("returnVal", p.typ, modeReturned)
+			g.genWrite("returnVal", p.typ, modeRetained)
 			g.Printf("return _returnVal;\n")
 		} else {
 			var rets []string
@@ -775,10 +775,10 @@ func (g *objcGen) genInterfaceMethodProxy(obj *types.TypeName, m *types.Func) {
 					g.Printf("}\n")
 					g.Outdent()
 					g.Printf("}\n")
-					g.genWrite(p.name+"_str", p.typ, modeReturned)
+					g.genWrite(p.name+"_str", p.typ, modeRetained)
 					rets = append(rets, fmt.Sprintf("_%s_str", p.name))
 				} else {
-					g.genWrite(p.name, p.typ, modeReturned)
+					g.genWrite(p.name, p.typ, modeRetained)
 					rets = append(rets, "_"+p.name)
 				}
 			}
@@ -808,7 +808,7 @@ func (g *objcGen) genRelease(varName string, t types.Type, mode varMode) {
 		case *types.Basic:
 			switch e.Kind() {
 			case types.Uint8: // Byte.
-				if !mode.copySlice() {
+				if mode == modeTransient {
 					// If the argument was not mutable, go_seq_from_objc_bytearray created a copy.
 					// Free it here.
 					g.Printf("if (![%s isKindOfClass:[NSMutableData class]]) {\n", varName)
diff --git a/bind/java/SeqBench.java b/bind/java/SeqBench.java
index 46a0f74..90e75a3 100644
--- a/bind/java/SeqBench.java
+++ b/bind/java/SeqBench.java
@@ -84,6 +84,16 @@ public class SeqBench extends InstrumentationTestCase {
           Benchmark.String(Benchmark.LongStringUnicode);
         }
       });
+      benchmarks.put("StringRetShort", new Runnable() {
+        @Override public void run() {
+          Benchmark.StringRetShort();
+        }
+      });
+      benchmarks.put("StringRetLong", new Runnable() {
+        @Override public void run() {
+          Benchmark.StringRetLong();
+        }
+      });
       final byte[] shortSlice = Benchmark.getShortSlice();
       benchmarks.put("SliceShort", new Runnable() {
         @Override public void run() {
@@ -138,6 +148,12 @@ public class SeqBench extends InstrumentationTestCase {
     }
     @Override public void Slice(byte[] s) {
     }
+	@Override public String StringRetShort() {
+		return Benchmark.ShortString;
+	}
+	@Override public String StringRetLong() {
+		return Benchmark.LongString;
+	}
   }
 
   public void testBenchmark() {
diff --git a/bind/java/SeqTest.java b/bind/java/SeqTest.java
index c252957..474591a 100644
--- a/bind/java/SeqTest.java
+++ b/bind/java/SeqTest.java
@@ -119,9 +119,25 @@ public class SeqTest extends InstrumentationTestCase {
     String[] tests = new String[]{
       "abcxyz09{}",
       "Hello, 世界",
-      "\uffff\uD800\uDC00\uD800\uDC01\uD808\uDF45\uDBFF\uDFFF"};
-    for (String want : tests) {
-      String got = Testpkg.StrDup(want);
+      "\uffff\uD800\uDC00\uD800\uDC01\uD808\uDF45\uDBFF\uDFFF",
+      // From Go std lib tests in unicode/utf16/utf16_test.go
+      "\u0001\u0002\u0003\u0004",
+      "\uffff\ud800\udc00\ud800\udc01\ud808\udf45\udbff\udfff",
+      "\ud800a",
+      "\udfff"
+    };
+    String[] wants = new String[]{
+      "abcxyz09{}",
+      "Hello, 世界",
+      "\uffff\uD800\uDC00\uD800\uDC01\uD808\uDF45\uDBFF\uDFFF",
+      "\u0001\u0002\u0003\u0004",
+      "\uffff\ud800\udc00\ud800\udc01\ud808\udf45\udbff\udfff",
+      "\ufffda",
+      "\ufffd"
+    };
+    for (int i = 0; i < tests.length; i++) {
+      String got = Testpkg.StrDup(tests[i]);
+      String want = wants[i];
       assertEquals("Strings should match", want, got);
     }
   }
diff --git a/bind/java/seq.h b/bind/java/seq.h
index 3514175..c6e16d3 100644
--- a/bind/java/seq.h
+++ b/bind/java/seq.h
@@ -14,12 +14,15 @@
 
 // Platform specific types
 typedef struct nstring {
-    void *chars; // utf16 encoded
-    jsize len; // length in bytes
+	// UTF16 or UTF8 Encoded string. When converting from Java string to Go
+	// string, UTF16. When converting from Go to Java, UTF8.
+	void *chars;
+	// length in bytes, regardless of encoding
+	jsize len;
 } nstring;
 typedef struct nbyteslice {
-    void *ptr;
-    jsize len;
+	void *ptr;
+	jsize len;
 } nbyteslice;
 typedef jlong nint;
 
@@ -34,7 +37,7 @@ extern jbyteArray go_seq_to_java_bytearray(JNIEnv *env, nbyteslice s, int copy);
 extern nbyteslice go_seq_from_java_bytearray(JNIEnv *env, jbyteArray s, int copy);
 
 extern jstring go_seq_to_java_string(JNIEnv *env, nstring str);
-extern nstring go_seq_from_java_string(JNIEnv *env, jstring s, int copy);
+extern nstring go_seq_from_java_string(JNIEnv *env, jstring s);
 
 // push_local_frame retrieves or creates the JNIEnv* for the current thread
 // and pushes a JNI reference frame. Must be matched with call to pop_local_frame.
diff --git a/bind/java/seq_android.c.support b/bind/java/seq_android.c.support
index 42d63dd..b1a095a 100644
--- a/bind/java/seq_android.c.support
+++ b/bind/java/seq_android.c.support
@@ -90,30 +90,108 @@ jbyteArray go_seq_to_java_bytearray(JNIEnv *env, nbyteslice s, int copy) {
 	return res;
 }
 
-nstring go_seq_from_java_string(JNIEnv *env, jstring str, int copy) {
+#define surr1 0xd800
+#define surr2 0xdc00
+#define surr3 0xe000
+
+// Unicode replacement character
+#define replacementChar 0xFFFD
+
+#define rune1Max ((1<<7) - 1)
+#define rune2Max ((1<<11) - 1)
+#define rune3Max ((1<<16) - 1)
+// Maximum valid Unicode code point.
+#define MaxRune 0x0010FFFF
+
+#define surrogateMin 0xD800
+#define surrogateMax 0xDFFF
+// 0011 1111
+#define maskx 0x3F
+// 1000 0000
+#define tx 0x80
+// 1100 0000
+#define t2 0xC0
+// 1110 0000
+#define t3 0xE0
+// 1111 0000
+#define t4 0xF0
+
+// encode_rune writes into p (which must be large enough) the UTF-8 encoding
+// of the rune. It returns the number of bytes written.
+static int encode_rune(uint8_t *p, uint32_t r) {
+	if (r <= rune1Max) {
+		p[0] = (uint8_t)r;
+		return 1;
+	} else if (r <= rune2Max) {
+		p[0] = t2 | (uint8_t)(r>>6);
+		p[1] = tx | (((uint8_t)(r))&maskx);
+		return 2;
+	} else {
+		if (r > MaxRune || (surrogateMin <= r && r <= surrogateMax)) {
+			r = replacementChar;
+		}
+		if (r <= rune3Max) {
+			p[0] = t3 | (uint8_t)(r>>12);
+			p[1] = tx | (((uint8_t)(r>>6))&maskx);
+			p[2] = tx | (((uint8_t)(r))&maskx);
+			return 3;
+		} else {
+			p[0] = t4 | (uint8_t)(r>>18);
+			p[1] = tx | (((uint8_t)(r>>12))&maskx);
+			p[2] = tx | (((uint8_t)(r>>6))&maskx);
+			p[3] = tx | (((uint8_t)(r))&maskx);
+			return 4;
+		}
+	}
+}
+
+// utf16_decode decodes an array of UTF16 characters to a UTF-8 encoded
+// nstring copy. The support functions and utf16_decode itself are heavily
+// based on the unicode/utf8 and unicode/utf16 Go packages.
+static nstring utf16_decode(jchar *chars, jsize len) {
+	jsize worstCaseLen = 4*len;
+	uint8_t *buf = malloc(worstCaseLen);
+	if (buf == NULL) {
+		LOG_FATAL("utf16Decode: malloc failed");
+	}
+	jsize nsrc = 0;
+	jsize ndst = 0;
+	while (nsrc < len) {
+		uint32_t r = chars[nsrc];
+		nsrc++;
+		if (surr1 <= r && r < surr2 && nsrc < len) {
+			uint32_t r2 = chars[nsrc];
+			if (surr2 <= r2 && r2 < surr3) {
+				nsrc++;
+				r = (((r-surr1)<<10) | (r2 - surr2)) + 0x10000;
+			}
+		}
+		if (ndst + 4 > worstCaseLen) {
+			LOG_FATAL("utf16Decode: buffer overflow");
+		}
+		ndst += encode_rune(buf + ndst, r);
+	}
+	struct nstring res = {chars: buf, len: ndst};
+	return res;
+}
+
+nstring go_seq_from_java_string(JNIEnv *env, jstring str) {
 	struct nstring res = {NULL, 0};
 	if (str == NULL) {
 		return res;
 	}
 	jsize nchars = (*env)->GetStringLength(env, str);
+	if (nchars == 0) {
+		return res;
+	}
 	jchar *chars = (jchar *)(*env)->GetStringChars(env, str, NULL);
 	if (chars == NULL) {
 		LOG_FATAL("GetStringChars failed");
 		return res;
 	}
-	if (copy) {
-		void *arr_copy = malloc(nchars*2);
-		if (arr_copy == NULL) {
-			LOG_FATAL("malloc failed");
-			return res;
-		}
-		memcpy(arr_copy, chars, nchars*2);
-		(*env)->ReleaseStringChars(env, str, chars);
-		chars = (jchar *)arr_copy;
-	}
-	res.chars = chars;
-	res.len = nchars;
-	return res;
+	nstring nstr = utf16_decode(chars, nchars);
+	(*env)->ReleaseStringChars(env, str, chars);
+	return nstr;
 }
 
 nbyteslice go_seq_from_java_bytearray(JNIEnv *env, jbyteArray arr, int copy) {
@@ -174,7 +252,7 @@ jobject go_seq_from_refnum(JNIEnv *env, int32_t refnum, jclass proxy_class, jmet
 
 // go_seq_to_java_string converts a nstring to a jstring.
 jstring go_seq_to_java_string(JNIEnv *env, nstring str) {
-	jstring s = (*env)->NewString(env, str.chars, str.len);
+	jstring s = (*env)->NewString(env, str.chars, str.len/2);
 	if (str.chars != NULL) {
 		free(str.chars);
 	}
diff --git a/bind/java/seq_android.go.support b/bind/java/seq_android.go.support
index 2b6c50b..d112159 100644
--- a/bind/java/seq_android.go.support
+++ b/bind/java/seq_android.go.support
@@ -15,7 +15,6 @@ package gomobile_bind
 //#include "seq.h"
 import "C"
 import (
-	"unicode/utf16"
 	"unsafe"
 
 	"golang.org/x/mobile/bind/seq"
@@ -27,13 +26,12 @@ func DestroyRef(refnum C.int32_t) {
 	seq.Delete(int32(refnum))
 }
 
-// encodeString encodes a Go string to utf16 and returns a Java string as a nstring
-// containing the jstring.
+// encodeString returns a copy of a Go string as a UTF16 encoded nstring.
+// The returned data is freed in go_seq_to_java_string.
+//
 // encodeString uses UTF16 as the intermediate format. Note that UTF8 is an obvious
 // alternative, but JNI only supports a C-safe variant of UTF8 (modified UTF8).
-// The returned data is always a copy, regardless of cpy, and will be freed in
-// go_seq_to_java_string.
-func encodeString(s string, cpy bool) C.nstring {
+func encodeString(s string) C.nstring {
 	n := C.int(len(s))
 	if n == 0 {
 		return C.nstring{}
@@ -46,20 +44,18 @@ func encodeString(s string, cpy bool) C.nstring {
 	}
 	chars := (*[1<<30 - 1]uint16)(unsafe.Pointer(utf16buf))[:worstCaseLen/2 : worstCaseLen/2]
 	nchars := seq.UTF16Encode(s, chars)
-	return C.nstring{chars: unsafe.Pointer(utf16buf), len: C.jsize(nchars)}
+	return C.nstring{chars: unsafe.Pointer(utf16buf), len: C.jsize(nchars*2)}
 }
 
-// decodeString decodes a nstring (jstring) to a Go string.
-// If cpy is set, the string contains a copy and is freed.
-func decodeString(str C.nstring, cpy bool) string {
+// decodeString decodes a UTF8 encoded nstring to a Go string. The data
+// in str is freed after use.
+func decodeString(str C.nstring) string {
 	if str.chars == nil {
 		return ""
 	}
-	chars := (*[1<<30 - 1]uint16)(unsafe.Pointer(str.chars))[:str.len]
-	s := string(utf16.Decode(chars)) // TODO: avoid the []rune allocation
-	if cpy {
-		C.free(str.chars)
-	}
+	chars := (*[1<<31 - 1]byte)(str.chars)[:str.len]
+	s := string(chars)
+	C.free(str.chars)
 	return s
 }
 
diff --git a/bind/objc/seq_darwin.go.support b/bind/objc/seq_darwin.go.support
index a494084..3e4412e 100644
--- a/bind/objc/seq_darwin.go.support
+++ b/bind/objc/seq_darwin.go.support
@@ -31,9 +31,7 @@ func DestroyRef(refnum C.int32_t) {
 }
 
 // encodeString copies a Go string and returns it as a nstring.
-// The result is always a copy, because go_seq_to_objc_string
-// uses NSString initWithBytesNoCopy to another copy.
-func encodeString(s string, cpy bool) C.nstring {
+func encodeString(s string) C.nstring {
 	n := C.int(len(s))
 	if n == 0 {
 		return C.nstring{}
@@ -46,10 +44,9 @@ func encodeString(s string, cpy bool) C.nstring {
 	return C.nstring{ptr: ptr, len: n}
 }
 
-// decodeString converts a nstring to a Go string.
-// The data in str is always a copy, so cpy is ignored
-// and the data is always freed.
-func decodeString(str C.nstring, cpy bool) string {
+// decodeString converts a nstring to a Go string. The
+// data in str is freed after use.
+func decodeString(str C.nstring) string {
 	if str.ptr == nil {
 		return ""
 	}
diff --git a/bind/seq/string.go b/bind/seq/string.go
index a39b115..b578d55 100644
--- a/bind/seq/string.go
+++ b/bind/seq/string.go
@@ -4,10 +4,7 @@
 
 package seq
 
-import (
-	"unicode/utf16"
-	"unsafe"
-)
+import "unicode/utf16"
 
 // Based heavily on package unicode/utf16 from the Go standard library.
 
@@ -27,10 +24,6 @@ const (
 	surrSelf = 0x10000
 )
 
-func writeUint16(b []byte, v rune) {
-	*(*uint16)(unsafe.Pointer(&b[0])) = uint16(v)
-}
-
 // UTF16Encode utf16 encodes s into chars. It returns the resulting
 // length in units of uint16. It is assumed that the chars slice
 // has enough room for the encoded string.
diff --git a/bind/testdata/basictypes.go.golden b/bind/testdata/basictypes.go.golden
index 89e6be7..a3eb955 100644
--- a/bind/testdata/basictypes.go.golden
+++ b/bind/testdata/basictypes.go.golden
@@ -49,7 +49,7 @@ func proxybasictypes__Error() C.nstring {
 	} else {
 		_res_0_str = res_0.Error()
 	}
-	_res_0 := encodeString(_res_0_str, true)
+	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
@@ -63,7 +63,7 @@ func proxybasictypes__ErrorPair() (C.nint, C.nstring) {
 	} else {
 		_res_1_str = res_1.Error()
 	}
-	_res_1 := encodeString(_res_1_str, true)
+	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
diff --git a/bind/testdata/interfaces.go.golden b/bind/testdata/interfaces.go.golden
index f55a960..4c53958 100644
--- a/bind/testdata/interfaces.go.golden
+++ b/bind/testdata/interfaces.go.golden
@@ -32,7 +32,7 @@ func proxyinterfaces_Error_Err(refnum C.int32_t) C.nstring {
 	} else {
 		_res_0_str = res_0.Error()
 	}
-	_res_0 := encodeString(_res_0_str, true)
+	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
@@ -40,7 +40,7 @@ type proxyinterfaces_Error _seq.Ref
 
 func (p *proxyinterfaces_Error) Err() error {
 	res := C.cproxyinterfaces_Error_Err(C.int32_t(p.Num))
-	_res_str := decodeString(res, true)
+	_res_str := decodeString(res)
 	_res := toError(_res_str)
 	return _res
 }
@@ -154,7 +154,7 @@ func proxyinterfaces__CallErr(param_e C.int32_t) C.nstring {
 	} else {
 		_res_0_str = res_0.Error()
 	}
-	_res_0 := encodeString(_res_0_str, true)
+	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
diff --git a/bind/testdata/interfaces.java.c.golden b/bind/testdata/interfaces.java.c.golden
index ba36f77..202c1fe 100644
--- a/bind/testdata/interfaces.java.c.golden
+++ b/bind/testdata/interfaces.java.c.golden
@@ -108,7 +108,7 @@ nstring cproxyinterfaces_Error_Err(int32_t refnum) {
     jobject o = go_seq_from_refnum(env, refnum, proxy_class_interfaces_Error, proxy_class_interfaces_Error_cons);
     (*env)->CallVoidMethod(env, o, mid_Error_Err);
     jstring exc = go_seq_get_exception_message(env);
-    nstring _exc = go_seq_from_java_string(env, exc, 1);
+    nstring _exc = go_seq_from_java_string(env, exc);
     go_seq_pop_local_frame(env);
     return _exc;
 }
diff --git a/bind/testdata/issue10788.go.golden b/bind/testdata/issue10788.go.golden
index 74e7d65..0981a16 100644
--- a/bind/testdata/issue10788.go.golden
+++ b/bind/testdata/issue10788.go.golden
@@ -26,7 +26,7 @@ type proxyTestStruct _seq.Ref
 //export proxyissue10788_TestStruct_Value_Set
 func proxyissue10788_TestStruct_Value_Set(refnum C.int32_t, v C.nstring) {
 	ref := _seq.FromRefNum(int32(refnum))
-	_v := decodeString(v, false)
+	_v := decodeString(v)
 	ref.Get().(*issue10788.TestStruct).Value = _v
 }
 
@@ -34,7 +34,7 @@ func proxyissue10788_TestStruct_Value_Set(refnum C.int32_t, v C.nstring) {
 func proxyissue10788_TestStruct_Value_Get(refnum C.int32_t) C.nstring {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(*issue10788.TestStruct).Value
-	_v := encodeString(v, true)
+	_v := encodeString(v)
 	return _v
 }
 
@@ -53,7 +53,7 @@ func proxyissue10788_TestInterface_MultipleUnnamedParams(refnum C.int32_t, param
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(issue10788.TestInterface)
 	_param_p0 := int(param_p0)
-	_param_p1 := decodeString(param_p1, false)
+	_param_p1 := decodeString(param_p1)
 	_param_p2 := int64(param_p2)
 	v.MultipleUnnamedParams(_param_p0, _param_p1, _param_p2)
 }
@@ -70,7 +70,7 @@ func (p *proxyissue10788_TestInterface) DoSomeWork(param_s *issue10788.TestStruc
 
 func (p *proxyissue10788_TestInterface) MultipleUnnamedParams(param_p0 int, param_p1 string, param_p2 int64) {
 	_param_p0 := C.nint(param_p0)
-	_param_p1 := encodeString(param_p1, false)
+	_param_p1 := encodeString(param_p1)
 	_param_p2 := C.int64_t(param_p2)
 	C.cproxyissue10788_TestInterface_MultipleUnnamedParams(C.int32_t(p.Num), _param_p0, _param_p1, _param_p2)
 }
diff --git a/bind/testdata/issue10788.java.c.golden b/bind/testdata/issue10788.java.c.golden
index 13da27c..9d63edc 100644
--- a/bind/testdata/issue10788.java.c.golden
+++ b/bind/testdata/issue10788.java.c.golden
@@ -35,11 +35,8 @@ Java_go_issue10788_Issue10788_init(JNIEnv *env, jclass _unused) {
 JNIEXPORT void JNICALL
 Java_go_issue10788_Issue10788_00024TestStruct_setValue(JNIEnv *env, jobject this, jstring v) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring _v = go_seq_from_java_string(env, v, 0);
+    nstring _v = go_seq_from_java_string(env, v);
     proxyissue10788_TestStruct_Value_Set(o, _v);
-    if (_v.chars != NULL) {
-      (*env)->ReleaseStringChars(env, v, _v.chars);
-    }
 }
 
 JNIEXPORT jstring JNICALL
@@ -69,12 +66,9 @@ JNIEXPORT void JNICALL
 Java_go_issue10788_Issue10788_00024TestInterface_00024Proxy_MultipleUnnamedParams(JNIEnv* env, jobject this, jlong p0, jstring p1, jlong p2) {
     int32_t o = go_seq_to_refnum(env, this);
     nint _p0 = (nint)p0;
-    nstring _p1 = go_seq_from_java_string(env, p1, 0);
+    nstring _p1 = go_seq_from_java_string(env, p1);
     int64_t _p2 = (int64_t)p2;
     proxyissue10788_TestInterface_MultipleUnnamedParams(o, _p0, _p1, _p2);
-    if (_p1.chars != NULL) {
-      (*env)->ReleaseStringChars(env, p1, _p1.chars);
-    }
 }
 
 void cproxyissue10788_TestInterface_MultipleUnnamedParams(int32_t refnum, nint p0, nstring p1, int64_t p2) {
diff --git a/bind/testdata/issue12328.go.golden b/bind/testdata/issue12328.go.golden
index fbcf4fa..65ce4c8 100644
--- a/bind/testdata/issue12328.go.golden
+++ b/bind/testdata/issue12328.go.golden
@@ -26,7 +26,7 @@ type proxyT _seq.Ref
 //export proxyissue12328_T_Err_Set
 func proxyissue12328_T_Err_Set(refnum C.int32_t, v C.nstring) {
 	ref := _seq.FromRefNum(int32(refnum))
-	_v_str := decodeString(v, false)
+	_v_str := decodeString(v)
 	_v := toError(_v_str)
 	ref.Get().(*issue12328.T).Err = _v
 }
@@ -41,6 +41,6 @@ func proxyissue12328_T_Err_Get(refnum C.int32_t) C.nstring {
 	} else {
 		_v_str = v.Error()
 	}
-	_v := encodeString(_v_str, true)
+	_v := encodeString(_v_str)
 	return _v
 }
diff --git a/bind/testdata/issue12328.java.c.golden b/bind/testdata/issue12328.java.c.golden
index 7fb843f..8aca32a 100644
--- a/bind/testdata/issue12328.java.c.golden
+++ b/bind/testdata/issue12328.java.c.golden
@@ -24,11 +24,8 @@ Java_go_issue12328_Issue12328_init(JNIEnv *env, jclass _unused) {
 JNIEXPORT void JNICALL
 Java_go_issue12328_Issue12328_00024T_setErr(JNIEnv *env, jobject this, jstring v) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring _v = go_seq_from_java_string(env, v, 0);
+    nstring _v = go_seq_from_java_string(env, v);
     proxyissue12328_T_Err_Set(o, _v);
-    if (_v.chars != NULL) {
-      (*env)->ReleaseStringChars(env, v, _v.chars);
-    }
 }
 
 JNIEXPORT jstring JNICALL
diff --git a/bind/testdata/issue12403.go.golden b/bind/testdata/issue12403.go.golden
index 585ee18..d0d3c6e 100644
--- a/bind/testdata/issue12403.go.golden
+++ b/bind/testdata/issue12403.go.golden
@@ -25,9 +25,9 @@ var _ = _seq.FromRefNum
 func proxyissue12403_Parsable_FromJSON(refnum C.int32_t, param_jstr C.nstring) C.nstring {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(issue12403.Parsable)
-	_param_jstr := decodeString(param_jstr, false)
+	_param_jstr := decodeString(param_jstr)
 	res_0 := v.FromJSON(_param_jstr)
-	_res_0 := encodeString(res_0, true)
+	_res_0 := encodeString(res_0)
 	return _res_0
 }
 
@@ -36,30 +36,30 @@ func proxyissue12403_Parsable_ToJSON(refnum C.int32_t) (C.nstring, C.nstring) {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(issue12403.Parsable)
 	res_0, res_1 := v.ToJSON()
-	_res_0 := encodeString(res_0, true)
+	_res_0 := encodeString(res_0)
 	var _res_1_str string
 	if res_1 == nil {
 		_res_1_str = ""
 	} else {
 		_res_1_str = res_1.Error()
 	}
-	_res_1 := encodeString(_res_1_str, true)
+	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
 type proxyissue12403_Parsable _seq.Ref
 
 func (p *proxyissue12403_Parsable) FromJSON(param_jstr string) string {
-	_param_jstr := encodeString(param_jstr, false)
+	_param_jstr := encodeString(param_jstr)
 	res := C.cproxyissue12403_Parsable_FromJSON(C.int32_t(p.Num), _param_jstr)
-	_res := decodeString(res, true)
+	_res := decodeString(res)
 	return _res
 }
 
 func (p *proxyissue12403_Parsable) ToJSON() (string, error) {
 	res := C.cproxyissue12403_Parsable_ToJSON(C.int32_t(p.Num))
-	res_0 := decodeString(res.r0, true)
-	res_1_str := decodeString(res.r1, true)
+	res_0 := decodeString(res.r0)
+	res_1_str := decodeString(res.r1)
 	res_1 := toError(res_1_str)
 	return res_0, res_1
 }
diff --git a/bind/testdata/issue12403.java.c.golden b/bind/testdata/issue12403.java.c.golden
index 511180f..b8d9e98 100644
--- a/bind/testdata/issue12403.java.c.golden
+++ b/bind/testdata/issue12403.java.c.golden
@@ -30,11 +30,8 @@ Java_go_issue12403_Issue12403_init(JNIEnv *env, jclass _unused) {
 JNIEXPORT jstring JNICALL
 Java_go_issue12403_Issue12403_00024Parsable_00024Proxy_FromJSON(JNIEnv* env, jobject this, jstring jstr) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring _jstr = go_seq_from_java_string(env, jstr, 0);
+    nstring _jstr = go_seq_from_java_string(env, jstr);
     nstring r0 = proxyissue12403_Parsable_FromJSON(o, _jstr);
-    if (_jstr.chars != NULL) {
-      (*env)->ReleaseStringChars(env, jstr, _jstr.chars);
-    }
     jstring _r0 = go_seq_to_java_string(env, r0);
     return _r0;
 }
@@ -44,7 +41,7 @@ nstring cproxyissue12403_Parsable_FromJSON(int32_t refnum, nstring jstr) {
     jobject o = go_seq_from_refnum(env, refnum, proxy_class_issue12403_Parsable, proxy_class_issue12403_Parsable_cons);
     jstring _jstr = go_seq_to_java_string(env, jstr);
     jstring res = (*env)->CallObjectMethod(env, o, mid_Parsable_FromJSON, _jstr);
-    nstring _res = go_seq_from_java_string(env, res, 1);
+    nstring _res = go_seq_from_java_string(env, res);
     go_seq_pop_local_frame(env);
     return _res;
 }
@@ -63,9 +60,9 @@ struct cproxyissue12403_Parsable_ToJSON_return cproxyissue12403_Parsable_ToJSON(
     JNIEnv *env = go_seq_push_local_frame(10);
     jobject o = go_seq_from_refnum(env, refnum, proxy_class_issue12403_Parsable, proxy_class_issue12403_Parsable_cons);
     jstring res = (*env)->CallObjectMethod(env, o, mid_Parsable_ToJSON);
-    nstring _res = go_seq_from_java_string(env, res, 1);
+    nstring _res = go_seq_from_java_string(env, res);
     jstring exc = go_seq_get_exception_message(env);
-    nstring _exc = go_seq_from_java_string(env, exc, 1);
+    nstring _exc = go_seq_from_java_string(env, exc);
     cproxyissue12403_Parsable_ToJSON_return sres = {
     	_res, _exc
     };
diff --git a/bind/testdata/structs.go.golden b/bind/testdata/structs.go.golden
index 69cc85b..4ec9ca0 100644
--- a/bind/testdata/structs.go.golden
+++ b/bind/testdata/structs.go.golden
@@ -68,7 +68,7 @@ func proxystructs_S_Identity(refnum C.int32_t) (C.int32_t, C.nstring) {
 	} else {
 		_res_1_str = res_1.Error()
 	}
-	_res_1 := encodeString(_res_1_str, true)
+	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
@@ -132,6 +132,6 @@ func proxystructs__IdentityWithError(param_s C.int32_t) (C.int32_t, C.nstring) {
 	} else {
 		_res_1_str = res_1.Error()
 	}
-	_res_1 := encodeString(_res_1_str, true)
+	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
diff --git a/bind/testdata/try.go.golden b/bind/testdata/try.go.golden
index e1df038..2dfe8e4 100644
--- a/bind/testdata/try.go.golden
+++ b/bind/testdata/try.go.golden
@@ -24,6 +24,6 @@ var _ = _seq.FromRefNum
 //export proxytry__This
 func proxytry__This() C.nstring {
 	res_0 := try.This()
-	_res_0 := encodeString(res_0, true)
+	_res_0 := encodeString(res_0)
 	return _res_0
 }
diff --git a/bind/testdata/vars.go.golden b/bind/testdata/vars.go.golden
index 5ef1baf..0f9c16e 100644
--- a/bind/testdata/vars.go.golden
+++ b/bind/testdata/vars.go.golden
@@ -82,14 +82,14 @@ func var_getvars_AFloat64() C.double {
 
 //export var_setvars_AString
 func var_setvars_AString(v C.nstring) {
-	_v := decodeString(v, false)
+	_v := decodeString(v)
 	vars.AString = _v
 }
 
 //export var_getvars_AString
 func var_getvars_AString() C.nstring {
 	v := vars.AString
-	_v := encodeString(v, true)
+	_v := encodeString(v)
 	return _v
 }
 
diff --git a/bind/testdata/vars.java.c.golden b/bind/testdata/vars.java.c.golden
index dedc189..7bbda6d 100644
--- a/bind/testdata/vars.java.c.golden
+++ b/bind/testdata/vars.java.c.golden
@@ -82,11 +82,8 @@ Java_go_vars_Vars_getAFloat64(JNIEnv *env, jclass clazz) {
 
 JNIEXPORT void JNICALL
 Java_go_vars_Vars_setAString(JNIEnv *env, jclass clazz, jstring v) {
-    nstring _v = go_seq_from_java_string(env, v, 0);
+    nstring _v = go_seq_from_java_string(env, v);
     var_setvars_AString(_v);
-    if (_v.chars != NULL) {
-      (*env)->ReleaseStringChars(env, v, _v.chars);
-    }
 }
 
 JNIEXPORT jstring JNICALL