diff --git a/src/leveldb/helpers/memenv/memenv.h b/src/leveldb/helpers/memenv/memenv.h
index ab5bde1..cba7a10 100644
--- a/src/leveldb/helpers/memenv/memenv.h
+++ b/src/leveldb/helpers/memenv/memenv.h
@@ -2,6 +2,19 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#ifndef __STDC_LIMIT_MACROS
-#define __STDC_LIMIT_MACROS
-#endif
+#ifndef STORAGE_LEVELDB_HELPERS_MEMENV_MEMENV_H__STDC_LIMIT_MACROS
+#define STORAGE_LEVELDB_HELPERS_MEMENV_MEMENV_H__STDC_LIMIT_MACROS
+
+namespace leveldb {
+
+class Env;
+
+// Returns a new environment that stores its data in memory and delegates
+// all non-file-storage tasks to base_env. The caller must delete the result
+// when it is no longer needed.
+// *base_env must remain live while the result is in use.
+Env* NewMemEnv(Env* base_env);
+
+}  // namespace leveldb
+
+#endif  // STORAGE_LEVELDB_HELPERS_MEMENV_MEMENV_H_