diff --git a/bind/genobjc.go b/bind/genobjc.go
index a928989..7595fa0 100644
--- a/bind/genobjc.go
+++ b/bind/genobjc.go
@@ -198,7 +198,7 @@ func (g *ObjcGen) GenH() error {
 		g.objcdoc(g.docs[obj.Name()].Doc())
 		switch b := obj.Type().(*types.Basic); b.Kind() {
 		case types.String, types.UntypedString:
-			g.Printf("FOUNDATION_EXPORT NSString* const %s%s;\n", g.namePrefix, obj.Name())
+			g.Printf("FOUNDATION_EXPORT NSString* _Nonnull const %s%s;\n", g.namePrefix, obj.Name())
 		default:
 			g.Printf("FOUNDATION_EXPORT const %s %s%s;\n", g.objcType(obj.Type()), g.namePrefix, obj.Name())
 		}
@@ -545,7 +545,7 @@ func (s *funcSummary) asFunc(g *ObjcGen) string {
 		skip = 1
 	}
 	for _, p := range s.retParams[skip:] {
-		params = append(params, g.objcType(p.typ)+"* "+p.name)
+		params = append(params, g.objcType(p.typ)+"* _Nullable "+p.name)
 	}
 	paramContents := "void"
 	if len(params) > 0 {
@@ -580,7 +580,7 @@ func (s *funcSummary) asSignature(g *ObjcGen) string {
 		if len(params) > 0 {
 			key = p.name
 		}
-		params = append(params, fmt.Sprintf("%s:(%s)%s", key, g.objcType(p.typ)+"*", p.name))
+		params = append(params, fmt.Sprintf("%s:(%s)%s", key, g.objcType(p.typ)+"* _Nullable", p.name))
 	}
 	return strings.Join(params, " ")
 }
@@ -878,9 +878,9 @@ func (g *ObjcGen) genInterfaceInterface(obj *types.TypeName, summary ifaceSummar
 	}
 	g.Printf(" <%s>", strings.Join(prots, ", "))
 	g.Printf(" {\n}\n")
-	g.Printf("@property(strong, readonly) id _ref;\n")
+	g.Printf("@property(strong, readonly) _Nonnull id _ref;\n")
 	g.Printf("\n")
-	g.Printf("- (instancetype)initWithRef:(id)ref;\n")
+	g.Printf("- (nonnull instancetype)initWithRef:(_Nonnull id)ref;\n")
 	for _, m := range summary.callable {
 		if !g.isSigSupported(m.Type()) {
 			g.Printf("// skipped method %s.%s with unsupported parameter or return types\n\n", obj.Name(), m.Name())
@@ -918,7 +918,7 @@ func (g *ObjcGen) genInterfaceM(obj *types.TypeName, t *types.Interface) bool {
 	g.Printf("@implementation %s%s {\n", g.namePrefix, obj.Name())
 	g.Printf("}\n")
 	g.Printf("\n")
-	g.Printf("- (instancetype)initWithRef:(id)ref {\n")
+	g.Printf("- (nonnull instancetype)initWithRef:(id)ref {\n")
 	g.Indent()
 	if isErrorType(obj.Type()) {
 		g.Printf("if (self) {\n")
@@ -1097,9 +1097,9 @@ func (g *ObjcGen) genStructH(obj *types.TypeName, t *types.Struct) {
 	}
 	g.Printf(" {\n")
 	g.Printf("}\n")
-	g.Printf("@property(strong, readonly) id _ref;\n")
+	g.Printf("@property(strong, readonly) _Nonnull id _ref;\n")
 	g.Printf("\n")
-	g.Printf("- (nonnull instancetype)initWithRef:(id)ref;\n")
+	g.Printf("- (nonnull instancetype)initWithRef:(_Nonnull id)ref;\n")
 	cons := g.constructors[obj]
 	if oinf == nil {
 		for _, f := range cons {
@@ -1156,7 +1156,7 @@ func (g *ObjcGen) genStructM(obj *types.TypeName, t *types.Struct) {
 	oinf := g.ostructs[obj]
 	g.Printf("@implementation %s%s {\n", g.namePrefix, obj.Name())
 	g.Printf("}\n\n")
-	g.Printf("- (instancetype)initWithRef:(id)ref {\n")
+	g.Printf("- (nonnull instancetype)initWithRef:(_Nonnull id)ref {\n")
 	g.Indent()
 	g.Printf("self = [super init];\n")
 	g.Printf("if (self) { __ref = ref; }\n")
@@ -1174,7 +1174,7 @@ func (g *ObjcGen) genStructM(obj *types.TypeName, t *types.Struct) {
 		}
 	}
 	if oinf != nil || len(cons) == 0 {
-		g.Printf("- (instancetype)init {\n")
+		g.Printf("- (nonnull instancetype)init {\n")
 		g.Indent()
 		g.Printf("self = [super init];\n")
 		g.Printf("if (self) {\n")
diff --git a/bind/testdata/basictypes.objc.h.golden b/bind/testdata/basictypes.objc.h.golden
index 134bbcf..246b6b1 100644
--- a/bind/testdata/basictypes.objc.h.golden
+++ b/bind/testdata/basictypes.objc.h.golden
@@ -13,9 +13,9 @@
 
 FOUNDATION_EXPORT const BOOL BasictypesABool;
 FOUNDATION_EXPORT const double BasictypesAFloat;
-FOUNDATION_EXPORT NSString* const BasictypesALongString;
+FOUNDATION_EXPORT NSString* _Nonnull const BasictypesALongString;
 FOUNDATION_EXPORT const int32_t BasictypesARune;
-FOUNDATION_EXPORT NSString* const BasictypesAString;
+FOUNDATION_EXPORT NSString* _Nonnull const BasictypesAString;
 FOUNDATION_EXPORT const int64_t BasictypesAnInt;
 FOUNDATION_EXPORT const int64_t BasictypesAnInt2;
 
@@ -23,9 +23,9 @@ FOUNDATION_EXPORT BOOL BasictypesBool(BOOL p0);
 
 FOUNDATION_EXPORT NSData* _Nullable BasictypesByteArrays(NSData* _Nullable x);
 
-FOUNDATION_EXPORT BOOL BasictypesError(NSError* _Nullable* error);
+FOUNDATION_EXPORT BOOL BasictypesError(NSError* _Nullable* _Nullable error);
 
-FOUNDATION_EXPORT BOOL BasictypesErrorPair(long* ret0_, NSError* _Nullable* error);
+FOUNDATION_EXPORT BOOL BasictypesErrorPair(long* _Nullable ret0_, NSError* _Nullable* _Nullable error);
 
 FOUNDATION_EXPORT void BasictypesInts(int8_t x, int16_t y, int32_t z, int64_t t, long u);
 
diff --git a/bind/testdata/basictypes.objc.m.golden b/bind/testdata/basictypes.objc.m.golden
index 9e907ed..b467759 100644
--- a/bind/testdata/basictypes.objc.m.golden
+++ b/bind/testdata/basictypes.objc.m.golden
@@ -34,7 +34,7 @@ NSData* _Nullable BasictypesByteArrays(NSData* _Nullable x) {
 	return _ret0_;
 }
 
-BOOL BasictypesError(NSError* _Nullable* error) {
+BOOL BasictypesError(NSError* _Nullable* _Nullable error) {
 	int32_t r0 = proxybasictypes__Error();
 	Universeerror* _error = nil;
 	GoSeqRef* _error_ref = go_seq_from_refnum(r0);
@@ -50,7 +50,7 @@ BOOL BasictypesError(NSError* _Nullable* error) {
 	return (_error == nil);
 }
 
-BOOL BasictypesErrorPair(long* ret0_, NSError* _Nullable* error) {
+BOOL BasictypesErrorPair(long* _Nullable ret0_, NSError* _Nullable* _Nullable error) {
 	struct proxybasictypes__ErrorPair_return res = proxybasictypes__ErrorPair();
 	long _ret0_ = (long)res.r0;
 	Universeerror* _error = nil;
diff --git a/bind/testdata/doc.objc.h.golden b/bind/testdata/doc.objc.h.golden
index 0754847..9279a10 100644
--- a/bind/testdata/doc.objc.h.golden
+++ b/bind/testdata/doc.objc.h.golden
@@ -26,9 +26,9 @@
  */
 @interface DocNoDoc : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @end
 
@@ -37,9 +37,9 @@
  */
 @interface DocS : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 /**
  * NewS is a constructor.
  */
@@ -72,9 +72,9 @@
  */
 @interface DocS2 : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @end
 
@@ -121,9 +121,9 @@ FOUNDATION_EXPORT DocS* _Nullable DocNewS(void);
  */
 @interface DocI : NSObject <goSeqRefInterface, DocI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 /**
  * IM is a method.
  */
diff --git a/bind/testdata/doc.objc.m.golden b/bind/testdata/doc.objc.m.golden
index ebb201a..cb8c7c8 100644
--- a/bind/testdata/doc.objc.m.golden
+++ b/bind/testdata/doc.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation DocNoDoc {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_doc_NoDoc());
@@ -33,7 +33,7 @@
 @implementation DocS {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -129,13 +129,13 @@
 @implementation DocS2 {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_doc_S2());
@@ -149,7 +149,7 @@
 @implementation DocI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
diff --git a/bind/testdata/ignore.objc.h.golden b/bind/testdata/ignore.objc.h.golden
index b4b23d7..bcb03df 100644
--- a/bind/testdata/ignore.objc.h.golden
+++ b/bind/testdata/ignore.objc.h.golden
@@ -24,9 +24,9 @@
 
 @interface IgnoreS : NSObject <goSeqRefInterface, IgnoreI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 // skipped field S.F with unsupported type: interface{}
 
@@ -72,9 +72,9 @@
 
 @interface IgnoreI : NSObject <goSeqRefInterface, IgnoreI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 // skipped method I.Argument with unsupported parameter or return types
 
 // skipped method I.Result with unsupported parameter or return types
diff --git a/bind/testdata/ignore.objc.m.golden b/bind/testdata/ignore.objc.m.golden
index 074cbce..2415812 100644
--- a/bind/testdata/ignore.objc.m.golden
+++ b/bind/testdata/ignore.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation IgnoreS {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_ignore_S());
@@ -38,7 +38,7 @@
 @implementation IgnoreI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
diff --git a/bind/testdata/interfaces.objc.h.golden b/bind/testdata/interfaces.objc.h.golden
index a25f498..ed5c507 100644
--- a/bind/testdata/interfaces.objc.h.golden
+++ b/bind/testdata/interfaces.objc.h.golden
@@ -29,7 +29,7 @@
 @class InterfacesWithParam;
 
 @protocol InterfacesError <NSObject>
-- (BOOL)err:(NSError* _Nullable*)error;
+- (BOOL)err:(NSError* _Nullable* _Nullable)error;
 @end
 
 @protocol InterfacesI <NSObject>
@@ -41,9 +41,9 @@
  */
 @interface InterfacesI1 : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)j;
 @end
 
@@ -52,9 +52,9 @@
  */
 @interface InterfacesI2 : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)g;
 @end
 
@@ -81,7 +81,7 @@
 
 FOUNDATION_EXPORT int32_t InterfacesAdd3(id<InterfacesI> _Nullable r);
 
-FOUNDATION_EXPORT BOOL InterfacesCallErr(id<InterfacesError> _Nullable e, NSError* _Nullable* error);
+FOUNDATION_EXPORT BOOL InterfacesCallErr(id<InterfacesError> _Nullable e, NSError* _Nullable* _Nullable error);
 
 FOUNDATION_EXPORT id<InterfacesI> _Nullable InterfacesSeven(void);
 
@@ -101,17 +101,17 @@ FOUNDATION_EXPORT id<InterfacesI> _Nullable InterfacesSeven(void);
 
 @interface InterfacesError : NSObject <goSeqRefInterface, InterfacesError> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
-- (BOOL)err:(NSError* _Nullable*)error;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
+- (BOOL)err:(NSError* _Nullable* _Nullable)error;
 @end
 
 @interface InterfacesI : NSObject <goSeqRefInterface, InterfacesI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (int32_t)rand;
 @end
 
@@ -121,9 +121,9 @@ FOUNDATION_EXPORT id<InterfacesI> _Nullable InterfacesSeven(void);
  */
 @interface InterfacesI3 : NSObject <goSeqRefInterface, InterfacesI3> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (InterfacesI1* _Nullable)f;
 @end
 
@@ -132,34 +132,34 @@ FOUNDATION_EXPORT id<InterfacesI> _Nullable InterfacesSeven(void);
  */
 @interface InterfacesInterfaces : NSObject <goSeqRefInterface, InterfacesInterfaces> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)someMethod;
 @end
 
 @interface InterfacesLargerI : NSObject <goSeqRefInterface, InterfacesLargerI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)anotherFunc;
 - (int32_t)rand;
 @end
 
 @interface InterfacesSameI : NSObject <goSeqRefInterface, InterfacesSameI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (int32_t)rand;
 @end
 
 @interface InterfacesWithParam : NSObject <goSeqRefInterface, InterfacesWithParam> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)hasParam:(BOOL)p0;
 @end
 
diff --git a/bind/testdata/interfaces.objc.m.golden b/bind/testdata/interfaces.objc.m.golden
index da83529..6148d5a 100644
--- a/bind/testdata/interfaces.objc.m.golden
+++ b/bind/testdata/interfaces.objc.m.golden
@@ -11,13 +11,13 @@
 @implementation InterfacesError {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (BOOL)err:(NSError* _Nullable*)error {
+- (BOOL)err:(NSError* _Nullable* _Nullable)error {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
 	int32_t r0 = proxyinterfaces_Error_Err(refnum);
 	Universeerror* _error = nil;
@@ -40,7 +40,7 @@
 @implementation InterfacesI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -59,7 +59,7 @@
 @implementation InterfacesI1 {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -76,7 +76,7 @@
 @implementation InterfacesI2 {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -93,7 +93,7 @@
 @implementation InterfacesI3 {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -119,7 +119,7 @@
 @implementation InterfacesInterfaces {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -136,7 +136,7 @@
 @implementation InterfacesLargerI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -160,7 +160,7 @@
 @implementation InterfacesSameI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -179,7 +179,7 @@
 @implementation InterfacesWithParam {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -208,7 +208,7 @@ int32_t InterfacesAdd3(id<InterfacesI> _Nullable r) {
 	return _ret0_;
 }
 
-BOOL InterfacesCallErr(id<InterfacesError> _Nullable e, NSError* _Nullable* error) {
+BOOL InterfacesCallErr(id<InterfacesError> _Nullable e, NSError* _Nullable* _Nullable error) {
 	int32_t _e;
 	if ([e conformsToProtocol:@protocol(goSeqRefInterface)]) {
 		id<goSeqRefInterface> e_proxy = (id<goSeqRefInterface>)(e);
diff --git a/bind/testdata/issue10788.objc.h.golden b/bind/testdata/issue10788.objc.h.golden
index fed5085..556560d 100644
--- a/bind/testdata/issue10788.objc.h.golden
+++ b/bind/testdata/issue10788.objc.h.golden
@@ -22,9 +22,9 @@
 
 @interface Issue10788TestStruct : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @property (nonatomic) NSString* _Nonnull value;
 @end
@@ -33,9 +33,9 @@
 
 @interface Issue10788TestInterface : NSObject <goSeqRefInterface, Issue10788TestInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)doSomeWork:(Issue10788TestStruct* _Nullable)s;
 - (void)multipleUnnamedParams:(long)p0 p1:(NSString* _Nullable)p1 日本:(int64_t)日本;
 @end
diff --git a/bind/testdata/issue10788.objc.m.golden b/bind/testdata/issue10788.objc.m.golden
index c218e33..8aad517 100644
--- a/bind/testdata/issue10788.objc.m.golden
+++ b/bind/testdata/issue10788.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation Issue10788TestStruct {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_issue10788_TestStruct());
@@ -45,7 +45,7 @@
 @implementation Issue10788TestInterface {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
diff --git a/bind/testdata/issue12328.objc.h.golden b/bind/testdata/issue12328.objc.h.golden
index 3fb9333..d81f503 100644
--- a/bind/testdata/issue12328.objc.h.golden
+++ b/bind/testdata/issue12328.objc.h.golden
@@ -15,9 +15,9 @@
 
 @interface Issue12328T : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @property (nonatomic) NSError* _Nullable err;
 @end
diff --git a/bind/testdata/issue12328.objc.m.golden b/bind/testdata/issue12328.objc.m.golden
index 6f2c9b7..08adc6a 100644
--- a/bind/testdata/issue12328.objc.m.golden
+++ b/bind/testdata/issue12328.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation Issue12328T {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_issue12328_T());
diff --git a/bind/testdata/issue12403.objc.h.golden b/bind/testdata/issue12403.objc.h.golden
index bfc6d04..8710fb7 100644
--- a/bind/testdata/issue12403.objc.h.golden
+++ b/bind/testdata/issue12403.objc.h.golden
@@ -16,18 +16,18 @@
 
 @protocol Issue12403Parsable <NSObject>
 - (NSString* _Nonnull)fromJSON:(NSString* _Nullable)jstr;
-- (NSString* _Nonnull)toJSON:(NSError* _Nullable*)error;
+- (NSString* _Nonnull)toJSON:(NSError* _Nullable* _Nullable)error;
 @end
 
 @class Issue12403Parsable;
 
 @interface Issue12403Parsable : NSObject <goSeqRefInterface, Issue12403Parsable> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (NSString* _Nonnull)fromJSON:(NSString* _Nullable)jstr;
-- (NSString* _Nonnull)toJSON:(NSError* _Nullable*)error;
+- (NSString* _Nonnull)toJSON:(NSError* _Nullable* _Nullable)error;
 @end
 
 #endif
diff --git a/bind/testdata/issue12403.objc.m.golden b/bind/testdata/issue12403.objc.m.golden
index 8d62c88..4e9b14c 100644
--- a/bind/testdata/issue12403.objc.m.golden
+++ b/bind/testdata/issue12403.objc.m.golden
@@ -11,7 +11,7 @@
 @implementation Issue12403Parsable {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -25,7 +25,7 @@
 	return _ret0_;
 }
 
-- (NSString* _Nonnull)toJSON:(NSError* _Nullable*)error {
+- (NSString* _Nonnull)toJSON:(NSError* _Nullable* _Nullable)error {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
 	struct proxyissue12403_Parsable_ToJSON_return res = proxyissue12403_Parsable_ToJSON(refnum);
 	NSString *_ret0_ = go_seq_to_objc_string(res.r0);
diff --git a/bind/testdata/keywords.objc.h.golden b/bind/testdata/keywords.objc.h.golden
index 4fa7864..67430b1 100644
--- a/bind/testdata/keywords.objc.h.golden
+++ b/bind/testdata/keywords.objc.h.golden
@@ -80,9 +80,9 @@ FOUNDATION_EXPORT void KeywordsStatic(NSString* _Nullable strictfp);
 
 @interface KeywordsKeywordCaller : NSObject <goSeqRefInterface, KeywordsKeywordCaller> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)abstract;
 - (void)assert;
 - (void)bool_;
diff --git a/bind/testdata/keywords.objc.m.golden b/bind/testdata/keywords.objc.m.golden
index 21dbdb1..881332b 100644
--- a/bind/testdata/keywords.objc.m.golden
+++ b/bind/testdata/keywords.objc.m.golden
@@ -11,7 +11,7 @@
 @implementation KeywordsKeywordCaller {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
diff --git a/bind/testdata/structs.objc.h.golden b/bind/testdata/structs.objc.h.golden
index 244cfd3..87ccbc0 100644
--- a/bind/testdata/structs.objc.h.golden
+++ b/bind/testdata/structs.objc.h.golden
@@ -23,21 +23,21 @@
 
 @interface StructsS : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @property (nonatomic) double x;
 @property (nonatomic) double y;
-- (StructsS* _Nullable)identity:(NSError* _Nullable*)error;
+- (StructsS* _Nullable)identity:(NSError* _Nullable* _Nullable)error;
 - (double)sum;
 @end
 
 @interface StructsS2 : NSObject <goSeqRefInterface, StructsI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 - (void)m;
 - (NSString* _Nonnull)string;
@@ -48,24 +48,24 @@
  */
 @interface StructsStructs : NSObject <goSeqRefInterface, StructsI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 - (void)m;
 @end
 
 FOUNDATION_EXPORT StructsS* _Nullable StructsIdentity(StructsS* _Nullable s);
 
-FOUNDATION_EXPORT StructsS* _Nullable StructsIdentityWithError(StructsS* _Nullable s, NSError* _Nullable* error);
+FOUNDATION_EXPORT StructsS* _Nullable StructsIdentityWithError(StructsS* _Nullable s, NSError* _Nullable* _Nullable error);
 
 @class StructsI;
 
 @interface StructsI : NSObject <goSeqRefInterface, StructsI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (void)m;
 @end
 
diff --git a/bind/testdata/structs.objc.m.golden b/bind/testdata/structs.objc.m.golden
index dec7196..c865174 100644
--- a/bind/testdata/structs.objc.m.golden
+++ b/bind/testdata/structs.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation StructsS {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_structs_S());
@@ -52,7 +52,7 @@
 	proxystructs_S_Y_Set(refnum, _v);
 }
 
-- (StructsS* _Nullable)identity:(NSError* _Nullable*)error {
+- (StructsS* _Nullable)identity:(NSError* _Nullable* _Nullable)error {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
 	struct proxystructs_S_Identity_return res = proxystructs_S_Identity(refnum);
 	StructsS* _ret0_ = nil;
@@ -94,13 +94,13 @@
 @implementation StructsS2 {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_structs_S2());
@@ -127,13 +127,13 @@
 @implementation StructsStructs {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_structs_Structs());
@@ -152,7 +152,7 @@
 @implementation StructsI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
@@ -187,7 +187,7 @@ StructsS* _Nullable StructsIdentity(StructsS* _Nullable s) {
 	return _ret0_;
 }
 
-StructsS* _Nullable StructsIdentityWithError(StructsS* _Nullable s, NSError* _Nullable* error) {
+StructsS* _Nullable StructsIdentityWithError(StructsS* _Nullable s, NSError* _Nullable* _Nullable error) {
 	int32_t _s;
 	if ([s conformsToProtocol:@protocol(goSeqRefInterface)]) {
 		id<goSeqRefInterface> s_proxy = (id<goSeqRefInterface>)(s);
diff --git a/bind/testdata/underscores.objc.h.golden b/bind/testdata/underscores.objc.h.golden
index 56e922b..3daaec0 100644
--- a/bind/testdata/underscores.objc.h.golden
+++ b/bind/testdata/underscores.objc.h.golden
@@ -15,9 +15,9 @@
 
 @interface Underscore_pkgUnderscore_struct : NSObject <goSeqRefInterface> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @property (nonatomic) NSString* _Nonnull underscore_field;
 @end
diff --git a/bind/testdata/underscores.objc.m.golden b/bind/testdata/underscores.objc.m.golden
index 116b28b..a985755 100644
--- a/bind/testdata/underscores.objc.m.golden
+++ b/bind/testdata/underscores.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation Underscore_pkgUnderscore_struct {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_underscore_pkg_Underscore_struct());
diff --git a/bind/testdata/universe.objc.h.golden b/bind/testdata/universe.objc.h.golden
index d0ee3dc..019e750 100644
--- a/bind/testdata/universe.objc.h.golden
+++ b/bind/testdata/universe.objc.h.golden
@@ -20,9 +20,9 @@
 
 @interface Universeerror : NSError <goSeqRefInterface, Universeerror> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (NSString* _Nonnull)error;
 @end
 
diff --git a/bind/testdata/universe.objc.m.golden b/bind/testdata/universe.objc.m.golden
index 0bfa3a2..369f238 100644
--- a/bind/testdata/universe.objc.m.golden
+++ b/bind/testdata/universe.objc.m.golden
@@ -11,7 +11,7 @@
 @implementation Universeerror {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	if (self) {
 		__ref = ref;
 		self = [super initWithDomain:@"go" code:1 userInfo:@{NSLocalizedDescriptionKey: [self error]}];
diff --git a/bind/testdata/vars.objc.h.golden b/bind/testdata/vars.objc.h.golden
index d1586de..569b375 100644
--- a/bind/testdata/vars.objc.h.golden
+++ b/bind/testdata/vars.objc.h.golden
@@ -20,9 +20,9 @@
 
 @interface VarsS : NSObject <goSeqRefInterface, VarsI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (nonnull instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 - (nonnull instancetype)init;
 @end
 
@@ -69,9 +69,9 @@
 
 @interface VarsI : NSObject <goSeqRefInterface, VarsI> {
 }
-@property(strong, readonly) id _ref;
+@property(strong, readonly) _Nonnull id _ref;
 
-- (instancetype)initWithRef:(id)ref;
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref;
 @end
 
 #endif
diff --git a/bind/testdata/vars.objc.m.golden b/bind/testdata/vars.objc.m.golden
index 9bc4f98..c390a84 100644
--- a/bind/testdata/vars.objc.m.golden
+++ b/bind/testdata/vars.objc.m.golden
@@ -12,13 +12,13 @@
 @implementation VarsS {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(_Nonnull id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;
 }
 
-- (instancetype)init {
+- (nonnull instancetype)init {
 	self = [super init];
 	if (self) {
 		__ref = go_seq_from_refnum(new_vars_S());
@@ -32,7 +32,7 @@
 @implementation VarsI {
 }
 
-- (instancetype)initWithRef:(id)ref {
+- (nonnull instancetype)initWithRef:(id)ref {
 	self = [super init];
 	if (self) { __ref = ref; }
 	return self;