diff --git a/lib/os.js b/lib/os.js
index 206e9941625965..cab148581a9db3 100644
--- a/lib/os.js
+++ b/lib/os.js
@@ -51,7 +51,8 @@ exports.tmpdir = function() {
   return path;
 };
 
-exports.tmpDir = exports.tmpdir;
+exports.tmpDir = internalUtil.deprecate(exports.tmpdir,
+    'os.tmpDir() is deprecated. Use os.tmpdir() instead.');
 
 exports.getNetworkInterfaces = internalUtil.deprecate(function() {
   return exports.networkInterfaces();