diff --git a/notimpl/readonly.cpp b/notimpl/readonly.cpp
new file mode 100644
index 0000000..f6ddad3
--- /dev/null
+++ b/notimpl/readonly.cpp
@@ -0,0 +1,30 @@
+/**
+ * Copyright 2017 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdexcept>
+
+#include "readonly.hpp"
+
+
+void ReadOnly::write(double value)
+{
+    throw std::runtime_error("Not supported.");
+}
+
+void ReadOnlyNoExcept::write(double value)
+{
+    return;
+}