--- a/js/src/vm/SavedStacks.h
+++ b/js/src/vm/SavedStacks.h
@@ -240,17 +240,17 @@ class SavedStacks {
 
     class MOZ_STACK_CLASS AutoFrameStateVector : public JS::CustomAutoRooter {
       public:
         explicit AutoFrameStateVector(JSContext *cx)
           : JS::CustomAutoRooter(cx),
             frames(cx)
         { }
 
-        typedef Vector<FrameState> FrameStateVector;
+        typedef Vector<FrameState, 20> FrameStateVector;
         inline FrameStateVector *operator->() { return &frames; }
         inline FrameState &operator[](size_t i) { return frames[i]; }
 
       private:
         FrameStateVector frames;
 
         virtual void trace(JSTracer *trc) {
             for (size_t i = 0; i < frames.length(); i++)