--- a/dom/canvas/TexUnpackBlob.cpp
+++ b/dom/canvas/TexUnpackBlob.cpp
@@ -634,16 +634,20 @@ TexUnpackImage::TexOrSubImage(bool isSub
     }
 
     const char* fallbackReason;
     do {
         if (mDepth != 1) {
             fallbackReason = "depth is not 1";
             break;
         }
+        if (xOffset != 0 || yOffset != 0 || zOffset != 0) {
+            fallbackReason = "x/y/zOffset is not 0";
+            break;
+        }
 
         if (webgl->mPixelStore_UnpackSkipPixels ||
             webgl->mPixelStore_UnpackSkipRows ||
             webgl->mPixelStore_UnpackSkipImages)
         {
             fallbackReason = "non-zero UNPACK_SKIP_* not yet supported";
             break;
         }