--- a/dom/canvas/WebGLRenderbuffer.cpp
+++ b/dom/canvas/WebGLRenderbuffer.cpp
@@ -273,17 +273,17 @@ WebGLRenderbuffer::GetRenderbufferParame
             gl->fBindRenderbuffer(LOCAL_GL_RENDERBUFFER, mPrimaryRB);
             GLint i = 0;
             gl->fGetRenderbufferParameteriv(target.get(), pname.get(), &i);
             return i;
         }
 
     case LOCAL_GL_RENDERBUFFER_INTERNAL_FORMAT:
         {
-            GLenum ret = 0;
+            GLenum ret = LOCAL_GL_RGBA4;
             if (mFormat) {
                 ret = mFormat->format->sizedFormat;
 
                 if (!mContext->IsWebGL2() && ret == LOCAL_GL_DEPTH24_STENCIL8) {
                     ret = LOCAL_GL_DEPTH_STENCIL;
                 }
             }
             return ret;