diff --git a/mozilla/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp b/mozilla/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
index 37476e88902..5d8eb9728f2 100644
--- a/mozilla/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
+++ b/mozilla/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
@@ -395,7 +395,7 @@ void nsGIFDecoder2::EndImageFrame()
   if (mGIFStruct.rows_remaining != mGIFStruct.height) {
     if (mGIFStruct.rows_remaining && mGIFStruct.images_decoded) {
       // Clear the remaining rows (only needed for the animation frames)
-      PRUint8 *rowp = mImageData + ((mGIFStruct.rows_remaining - mGIFStruct.height) * mGIFStruct.width);
+      PRUint8 *rowp = mImageData + ((mGIFStruct.height - mGIFStruct.rows_remaining) * mGIFStruct.width);
       memset(rowp, 0, mGIFStruct.rows_remaining * mGIFStruct.width);
     }