diff --git a/js/src/jscompartment.cpp b/js/src/jscompartment.cpp
index 0cf09b001a8..a7b0f729103 100644
--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -92,7 +92,8 @@ JSCompartment::JSCompartment(JSRuntime *rt)
     debugModeBits(rt->debugMode ? DebugFromC : 0),
     mathCache(NULL),
     watchpointMap(NULL),
-    scriptCountsMap(NULL)
+    scriptCountsMap(NULL),
+    sourceMapMap(NULL)
 {
     PodArrayZero(evalCache);
     setGCMaxMallocBytes(rt->gcMaxMallocBytes * 0.9);
@@ -113,6 +114,7 @@ JSCompartment::~JSCompartment()
     Foreground::delete_(mathCache);
     Foreground::delete_(watchpointMap);
     Foreground::delete_(scriptCountsMap);
+    Foreground::delete_(sourceMapMap);
 
 #ifdef DEBUG
     for (size_t i = 0; i < ArrayLength(evalCache); ++i)
diff --git a/js/src/jscompartment.h b/js/src/jscompartment.h
index ffa038377be..139c2c37765 100644
--- a/js/src/jscompartment.h
+++ b/js/src/jscompartment.h
@@ -465,6 +465,8 @@ struct JSCompartment
     js::WatchpointMap *watchpointMap;
 
     js::ScriptCountsMap *scriptCountsMap;
+
+    js::SourceMapMap *sourceMapMap;
 };
 
 #define JS_PROPERTY_TREE(cx)    ((cx)->compartment->propertyTree)
diff --git a/js/src/jsdbgapi.cpp b/js/src/jsdbgapi.cpp
index 728f4dc3b02..1277515dd7e 100644
--- a/js/src/jsdbgapi.cpp
+++ b/js/src/jsdbgapi.cpp
@@ -687,7 +687,7 @@ JS_GetScriptFilename(JSContext *cx, JSScript *script)
 JS_PUBLIC_API(const jschar *)
 JS_GetScriptSourceMap(JSContext *cx, JSScript *script)
 {
-    return script->sourceMap;
+    return script->hasSourceMap ? script->getSourceMap() : NULL;
 }
 
 JS_PUBLIC_API(unsigned)
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index f784e84efdd..24e5628a96a 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -880,6 +880,62 @@ JSScript::destroyScriptCounts(FreeOp *fop)
     }
 }
 
+bool
+JSScript::setSourceMap(JSContext *cx, jschar *sourceMap)
+{
+    JS_ASSERT(!hasSourceMap);
+
+    /* Create compartment's sourceMapMap if necessary. */
+    SourceMapMap *map = compartment()->sourceMapMap;
+    if (!map) {
+        map = cx->new_<SourceMapMap>();
+        if (!map || !map->init()) {
+            cx->delete_(map);
+            return false;
+        }
+        compartment()->sourceMapMap = map;
+    }
+
+    if (!map->putNew(this, sourceMap)) {
+        cx->delete_(map);
+        return false;
+    }
+    hasSourceMap = true; // safe to set this;  we can't fail after this point
+
+    return true;
+}
+
+jschar *
+JSScript::getSourceMap() {
+    JS_ASSERT(hasSourceMap);
+    SourceMapMap *map = compartment()->sourceMapMap;
+    JS_ASSERT(map);
+    SourceMapMap::Ptr p = map->lookup(this);
+    JS_ASSERT(p);
+    return p->value;
+}
+
+jschar *
+JSScript::releaseSourceMap()
+{
+    JS_ASSERT(hasSourceMap);
+    SourceMapMap *map = compartment()->sourceMapMap;
+    JS_ASSERT(map);
+    SourceMapMap::Ptr p = map->lookup(this);
+    JS_ASSERT(p);
+    jschar *sourceMap = p->value;
+    map->remove(p);
+    hasSourceMap = false;
+    return sourceMap;
+}
+
+void
+JSScript::destroySourceMap(FreeOp *fop)
+{
+    if (hasSourceMap)
+        fop->free_(releaseSourceMap());
+}
+
 /*
  * Shared script filename management.
  */
@@ -1287,7 +1343,13 @@ JSScript::NewScriptFromEmitter(JSContext *cx, BytecodeEmitter *bce)
     if (script->originPrincipals)
         JS_HoldPrincipals(script->originPrincipals);
 
-    script->sourceMap = (jschar *) bce->parser->tokenStream.releaseSourceMap();
+    jschar *sourceMap = (jschar *) bce->parser->tokenStream.releaseSourceMap();
+    if (sourceMap) {
+        if (!script->setSourceMap(cx, sourceMap)) {
+            cx->free_(sourceMap);
+            return NULL;
+        }
+    }
 
     if (!FinishTakingSrcNotes(cx, bce, script->notes()))
         return NULL;
@@ -1458,9 +1520,7 @@ JSScript::finalize(FreeOp *fop)
 #endif
 
     destroyScriptCounts(fop);
-
-    if (sourceMap)
-        fop->free_(sourceMap);
+    destroySourceMap(fop);
 
     if (debug) {
         jsbytecode *end = code + length;
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index d0fcdb1f418..38dd676d395 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -319,6 +319,11 @@ typedef HashMap<JSScript *,
                 DefaultHasher<JSScript *>,
                 SystemAllocPolicy> ScriptCountsMap;
 
+typedef HashMap<JSScript *,
+                jschar *,
+                DefaultHasher<JSScript *>,
+                SystemAllocPolicy> SourceMapMap;
+
 class DebugScript
 {
     friend struct ::JSScript;
@@ -421,8 +426,6 @@ struct JSScript : public js::gc::Cell
     JSPrincipals    *principals;/* principals for this script */
     JSPrincipals    *originPrincipals; /* see jsapi.h 'originPrincipals' comment */
 
-    jschar          *sourceMap; /* source map file or null */
-
     /*
      * A global object for the script.
      * - All scripts returned by JSAPI functions (JS_CompileScript,
@@ -469,13 +472,8 @@ struct JSScript : public js::gc::Cell
     // Unique identifier within the compartment for this script, used for
     // printing analysis information.
     uint32_t        id_;
- #if JS_BITS_PER_WORD == 64
   private:
-    uint32_t        idpad64;
- #endif
-#elif JS_BITS_PER_WORD == 32
-  private:
-    uint32_t        pad32;
+    uint32_t        idpad;
 #endif
 
     // 16-bit fields.
@@ -544,6 +542,8 @@ struct JSScript : public js::gc::Cell
     bool            isGenerator:1;    /* is a generator */
     bool            hasScriptCounts:1;/* script has an entry in
                                          JSCompartment::scriptCountsMap */
+    bool            hasSourceMap:1;   /* script has an entry in
+                                         JSCompartment::sourceMapMap */
 
   private:
     /* See comments below. */
@@ -695,12 +695,16 @@ struct JSScript : public js::gc::Cell
 #endif
 
   public:
-    js::PCCounts getPCCounts(jsbytecode *pc);
-
     bool initScriptCounts(JSContext *cx);
+    js::PCCounts getPCCounts(jsbytecode *pc);
     js::ScriptCounts releaseScriptCounts();
     void destroyScriptCounts(js::FreeOp *fop);
 
+    bool setSourceMap(JSContext *cx, jschar *sourceMap);
+    jschar *getSourceMap();
+    jschar *releaseSourceMap();
+    void destroySourceMap(js::FreeOp *fop);
+
     jsbytecode *main() {
         return code + mainOffset;
     }