diff --git a/src/starboard/shared/internal_only.h b/src/starboard/shared/internal_only.h
new file mode 100644
index 0000000..f5b5147
--- /dev/null
+++ b/src/starboard/shared/internal_only.h
@@ -0,0 +1,25 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// 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.
+
+// Should be included by internal headers - will assert that the header is only
+// included in starboard implementation files, and not publicly.
+
+#ifndef STARBOARD_SHARED_INTERNAL_ONLY_H_
+#define STARBOARD_SHARED_INTERNAL_ONLY_H_
+
+#if !defined(STARBOARD_IMPLEMENTATION)
+#error "This file cannot be included outside of a starboard implementation."
+#endif
+
+#endif  // STARBOARD_SHARED_INTERNAL_ONLY_H_