--- a/gfx/thebes/gfxUtils.cpp
+++ b/gfx/thebes/gfxUtils.cpp
@@ -1204,16 +1204,18 @@ gfxUtils::EncodeSourceSurface(SourceSurf
     if (imgSize == bufSize) {
       // need a bigger buffer, just double
       bufSize *= 2;
       if (!imgData.resizeUninitialized(bufSize)) {
         return NS_ERROR_OUT_OF_MEMORY;
       }
     }
   }
+  NS_ENSURE_SUCCESS(rv, rv);
+  NS_ENSURE_TRUE(!imgData.empty(), NS_ERROR_FAILURE);
 
   if (aBinaryOrData == eBinaryEncode) {
     if (aFile) {
       fwrite(imgData.begin(), 1, imgSize, aFile);
     }
     return NS_OK;
   }