diff --git a/src/node/src/metadata.js b/src/node/src/metadata.js
index a7b1ee3810d..d4a8b2669ff 100644
--- a/src/node/src/metadata.js
+++ b/src/node/src/metadata.js
@@ -49,14 +49,14 @@ function Metadata() {
 }
 
 function normalizeKey(key) {
+  if (!(/^[A-Za-z\d-]+$/.test(key))) {
+    throw new Error('Metadata keys must be nonempty strings containing only ' +
+        'alphanumeric characters and hyphens');
+  }
   return key.toLowerCase();
 }
 
 function validate(key, value) {
-  if (!(/^[a-z\d-]+$/.test(key))) {
-    throw new Error('Metadata keys must be nonempty strings containing only ' +
-        'alphanumeric characters and hyphens');
-  }
   if (_.endsWith(key, '-bin')) {
     if (!(value instanceof Buffer)) {
       throw new Error('keys that end with \'-bin\' must have Buffer values');