--- a/js/xpconnect/src/xpcpublic.h
+++ b/js/xpconnect/src/xpcpublic.h
@@ -16,16 +16,17 @@
 #include "nsIURI.h"
 #include "nsIPrincipal.h"
 #include "nsIGlobalObject.h"
 #include "nsPIDOMWindow.h"
 #include "nsWrapperCache.h"
 #include "nsStringGlue.h"
 #include "nsTArray.h"
 #include "mozilla/dom/JSSlots.h"
+#include "mozilla/fallible.h"
 #include "nsMathUtils.h"
 #include "nsStringBuffer.h"
 #include "mozilla/dom/BindingDeclarations.h"
 
 class nsGlobalWindow;
 class nsIPrincipal;
 class nsScriptNameSpaceManager;
 class nsIMemoryReporterCallback;
@@ -307,24 +308,32 @@ inline bool StringToJsval(JSContext* cx,
         return true;
     }
     return NonVoidStringToJsval(cx, str, rval);
 }
 
 inline bool
 NonVoidStringToJsval(JSContext* cx, const nsAString& str, JS::MutableHandleValue rval)
 {
-    nsString mutableCopy(str);
+    nsString mutableCopy;
+    if (!mutableCopy.Assign(str, mozilla::fallible)) {
+        JS_ReportOutOfMemory(cx);
+        return false;
+    }
     return NonVoidStringToJsval(cx, mutableCopy, rval);
 }
 
 inline bool
 StringToJsval(JSContext* cx, const nsAString& str, JS::MutableHandleValue rval)
 {
-    nsString mutableCopy(str);
+    nsString mutableCopy;
+    if (!mutableCopy.Assign(str, mozilla::fallible)) {
+        JS_ReportOutOfMemory(cx);
+        return false;
+    }
     return StringToJsval(cx, mutableCopy, rval);
 }
 
 /**
  * As above, but for mozilla::dom::DOMString.
  */
 MOZ_ALWAYS_INLINE
 bool NonVoidStringToJsval(JSContext* cx, mozilla::dom::DOMString& str,