--- a/dom/canvas/WebGLBuffer.cpp
+++ b/dom/canvas/WebGLBuffer.cpp
@@ -41,17 +41,19 @@ WebGLBuffer::BindTo(GLenum target)
     case LOCAL_GL_PIXEL_UNPACK_BUFFER:
     case LOCAL_GL_UNIFORM_BUFFER:
     case LOCAL_GL_TRANSFORM_FEEDBACK_BUFFER:
         mContent = Kind::OtherData;
         break;
 
     case LOCAL_GL_COPY_READ_BUFFER:
     case LOCAL_GL_COPY_WRITE_BUFFER:
-        /* Do nothing. Doesn't set the type of the buffer contents. */
+        if (mContent == Kind::Undefined) {
+          mContent = Kind::OtherData;
+        }
         break;
 
     default:
         MOZ_CRASH();
     }
 }
 
 void