diff --git a/src/users.js b/src/users.js
index ac44a9804..1eef61086 100644
--- a/src/users.js
+++ b/src/users.js
@@ -142,7 +142,7 @@ function validateUsername(username) {
     if (/[^a-zA-Z0-9.-]/.test(username)) return new BoxError(BoxError.BAD_FIELD, 'Username can only contain alphanumerals, dot and -');
 
     // app emails are sent using the .app suffix
-    if (username.indexOf('.app') !== -1) return new BoxError(BoxError.BAD_FIELD, 'Username pattern is reserved for apps');
+    if (username.endsWith('.app')) return new BoxError(BoxError.BAD_FIELD, 'Username pattern is reserved for apps');
 
     return null;
 }