diff --git a/config/locales/activerecord.en.yml b/config/locales/activerecord.en.yml
index 8533418c..728efa37 100644
--- a/config/locales/activerecord.en.yml
+++ b/config/locales/activerecord.en.yml
@@ -10,7 +10,7 @@ en:
         account:
           attributes:
             username:
-              invalid: only letters, numbers and underscores
+              invalid: Only letters, numbers and underscores. No spaces.
         status:
           attributes:
             reblog: