diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 445ab28e27b..e4df6e354d2 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -3714,7 +3714,12 @@ nsLayoutUtils::SurfaceFromElement(nsIDOMElement *aElement,
   result.mSurface = gfxsurf;
   result.mSize = gfxIntSize(imgWidth, imgHeight);
   result.mPrincipal = principal;
-  result.mIsWriteOnly = PR_FALSE;
+
+  // SVG images could have <foreignObject> and/or <image> elements that load
+  // content from another domain.  For safety, they make the canvas write-only.
+  // XXXdholbert We could probably be more permissive here if we check that our
+  // helper SVG document has no elements that could load remote content.
+  result.mIsWriteOnly = (imgContainer->GetType() == imgIContainer::TYPE_VECTOR);
 
   return result;
 }