--- a/js/src/jstypedarray.cpp
+++ b/js/src/jstypedarray.cpp
@@ -2915,18 +2915,21 @@ JSFunctionSpec _typedArray::jsfuncs[] = 
       MOZ_ASSERT(byteoffset <= INT32_MAX);                                                   \
       Rooted<JSObject*> arrayBuffer(cx, arrayBuffer_);                                       \
       Rooted<JSObject*> proto(cx, NULL);                                                     \
       return TypedArrayTemplate<NativeType>::fromBuffer(cx, arrayBuffer, byteoffset, length, \
                                                         proto);                              \
   }                                                                                          \
   JS_FRIEND_API(JSBool) JS_Is ## Name ## Array(JSObject *obj, JSContext *cx)                 \
   {                                                                                          \
-      if (!(obj = UnwrapObjectChecked(cx, obj)))                                             \
+      MOZ_ASSERT(!cx->isExceptionPending());                                                 \
+      if (!(obj = UnwrapObjectChecked(cx, obj))) {                                           \
+          cx->clearPendingException();                                                       \
           return false;                                                                      \
+      }                                                                                      \
       Class *clasp = obj->getClass();                                                        \
       return (clasp == &TypedArray::classes[TypedArrayTemplate<NativeType>::ArrayTypeID()]); \
   }
 
 IMPL_TYPED_ARRAY_JSAPI_CONSTRUCTORS(Int8, int8_t)
 IMPL_TYPED_ARRAY_JSAPI_CONSTRUCTORS(Uint8, uint8_t)
 IMPL_TYPED_ARRAY_JSAPI_CONSTRUCTORS(Uint8Clamped, uint8_clamped)
 IMPL_TYPED_ARRAY_JSAPI_CONSTRUCTORS(Int16, int16_t)