--- a/dom/canvas/WebGLTextureUpload.cpp
+++ b/dom/canvas/WebGLTextureUpload.cpp
@@ -257,16 +257,19 @@ WebGLTexture::TexOrSubImage(bool isSubIm
         }
 
         if (width && height && depth) {
             view.ComputeLengthAndData();
 
             bytes = view.DataAllowShared();
             byteCount = view.LengthAllowShared();
         }
+    } else if (isSubImage) {
+        mContext->ErrorInvalidValue("%s: `pixels` must not be null.", funcName);
+        return;
     }
 
     const bool isClientData = true;
     webgl::TexUnpackBytes blob(mContext, target, width, height, depth, isClientData,
                                bytes);
 
     if (bytes &&
         !ValidateUnpackBytes(mContext, funcName, width, height, depth, pi, byteCount,