--- a/layout/svg/SVGContextPaint.h
+++ b/layout/svg/SVGContextPaint.h
@@ -162,17 +162,18 @@ public:
     }
 
     union {
       nsSVGPaintServerFrame* mPaintServerFrame;
       SVGContextPaint* mContextPaint;
       nscolor mColor;
     } mPaintDefinition;
 
-    nsIFrame* mFrame;
+    // Initialized (if needed) in SetPaintServer():
+    MOZ_INIT_OUTSIDE_CTOR nsIFrame* mFrame;
     // CTM defining the user space for the pattern we will use.
     gfxMatrix mContextMatrix;
     nsStyleSVGPaintType mPaintType;
 
     // Device-space-to-pattern-space
     gfxMatrix mPatternMatrix;
     nsRefPtrHashtable<nsFloatHashKey, gfxPattern> mPatternCache;