diff --git a/moku/forms/auth.py b/moku/forms/auth.py
new file mode 100644
index 0000000..88a503f
--- /dev/null
+++ b/moku/forms/auth.py
@@ -0,0 +1,12 @@
+from django.contrib.auth.forms import AuthenticationForm as BaseAuthenticationForm
+from django.utils.translation import gettext_lazy as _
+
+
+class AuthenticationForm(BaseAuthenticationForm):
+    error_messages = {
+        "invalid_login": _("sorry! that username and password didn't work."),
+        "inactive": _("your account has been deactivated."),
+    }
+
+    def clean_username(self):
+        return self.cleaned_data.get("username").lower()
diff --git a/moku/views/auth.py b/moku/views/auth.py
index 6197a0b..5d42d65 100644
--- a/moku/views/auth.py
+++ b/moku/views/auth.py
@@ -5,6 +5,7 @@ from django.shortcuts import redirect
 from django.urls import reverse_lazy
 from django.utils.translation import gettext as _
 
+from moku.forms.auth import AuthenticationForm
 from moku.views.base import View
 
 
@@ -12,6 +13,7 @@ class LoginView(View, BaseLoginView):
     """Allows users to log in by username and password."""
 
     template_name = "moku/login.jinja"
+    form_class = AuthenticationForm
     page_title = "log in"
 
     def get(self, request, *args, **kwargs):