--- a/image/imgFrame.h
+++ b/image/imgFrame.h
@@ -473,16 +473,19 @@ class DrawableFrameRef final
   typedef gfx::DataSourceSurface DataSourceSurface;
 
 public:
   DrawableFrameRef() { }
 
   explicit DrawableFrameRef(imgFrame* aFrame)
     : mFrame(aFrame)
   {
+    MOZ_ASSERT(aFrame);
+    MonitorAutoLock lock(aFrame->mMonitor);
+
     // Paletted images won't have a surface so there is no strong reference
     // to hold on to. Since Draw() and GetSourceSurface() calls will not work
     // in that case, we should be using RawAccessFrameRef exclusively instead.
     // See FrameAnimator::GetRawFrame for an example of this behaviour.
     if (aFrame->mRawSurface) {
       mRef = new DataSourceSurface::ScopedMap(aFrame->mRawSurface,
                                               DataSourceSurface::READ_WRITE);
       if (!mRef->IsMapped()) {