--- a/gfx/layers/ThebesLayerBuffer.h
+++ b/gfx/layers/ThebesLayerBuffer.h
@@ -107,16 +107,20 @@ public:
    * mRegionToDraw must be drawn. mRegionToInvalidate has been invalidated
    * by ThebesLayerBuffer and must be redrawn on the screen.
    * mRegionToInvalidate is set when the buffer has changed from
    * opaque to transparent or vice versa, since the details of rendering can
    * depend on the buffer type.  mDidSelfCopy is true if we kept our buffer
    * but used MovePixels() to shift its content.
    */
   struct PaintState {
+    PaintState()
+      : mDidSelfCopy(PR_FALSE)
+    {}
+
     nsRefPtr<gfxContext> mContext;
     nsIntRegion mRegionToDraw;
     nsIntRegion mRegionToInvalidate;
     PRPackedBool mDidSelfCopy;
   };
 
   enum {
     PAINT_WILL_RESAMPLE = 0x01