diff --git a/layout/base/public/nsIStyleContext.h b/layout/base/public/nsIStyleContext.h
index c5b20cc05904..46c70431e4f0 100644
--- a/layout/base/public/nsIStyleContext.h
+++ b/layout/base/public/nsIStyleContext.h
@@ -342,6 +342,7 @@ struct nsBorderEdges
 inline nsBorderEdges::nsBorderEdges()
 {
   mMaxBorderWidth.SizeTo(0,0,0,0);
+  mOutsideEdge = PR_TRUE;
 };