diff --git a/dom/camera/CameraPreviewMediaStream.h b/dom/camera/CameraPreviewMediaStream.h
index 8d0ddd0007b..9dbff68991a 100644
--- a/dom/camera/CameraPreviewMediaStream.h
+++ b/dom/camera/CameraPreviewMediaStream.h
@@ -29,7 +29,8 @@ class CameraPreviewMediaStream : public MediaStream {
 public:
   CameraPreviewMediaStream(DOMMediaStream* aWrapper) :
     MediaStream(aWrapper),
-    mMutex("mozilla::camera::CameraPreviewMediaStream")
+    mMutex("mozilla::camera::CameraPreviewMediaStream"),
+    mFrameCallback(nullptr)
   {
     mIsConsumed = false;
   }