diff --git a/django/contrib/auth/forms.py b/django/contrib/auth/forms.py
index 5ffbc8207c..086acf3349 100644
--- a/django/contrib/auth/forms.py
+++ b/django/contrib/auth/forms.py
@@ -13,7 +13,7 @@ class UserCreationForm(forms.ModelForm):
     """
     username = forms.RegexField(label=_("Username"), max_length=30, regex=r'^[\w.@+-]+$',
         help_text = _("Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only."),
-        error_message = _("This value may contain only letters, numbers and @/./+/-/_ characters."))
+        error_messages = {'invalid': _("This value may contain only letters, numbers and @/./+/-/_ characters.")})
     password1 = forms.CharField(label=_("Password"), widget=forms.PasswordInput)
     password2 = forms.CharField(label=_("Password confirmation"), widget=forms.PasswordInput,
         help_text = _("Enter the same password as above, for verification."))
@@ -47,8 +47,8 @@ class UserCreationForm(forms.ModelForm):
 class UserChangeForm(forms.ModelForm):
     username = forms.RegexField(label=_("Username"), max_length=30, regex=r'^[\w.@+-]+$',
         help_text = _("Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only."),
-        error_message = _("This value may contain only letters, numbers and @/./+/-/_ characters."))
-    
+        error_messages = {'invalid': _("This value may contain only letters, numbers and @/./+/-/_ characters.")})
+
     class Meta:
         model = User