diff --git a/mozilla_django_oidc_db/models.py b/mozilla_django_oidc_db/models.py
index 7a672d8..a768f7b 100644
--- a/mozilla_django_oidc_db/models.py
+++ b/mozilla_django_oidc_db/models.py
@@ -3,7 +3,7 @@
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.contrib.auth.models import Group
-from django.core.exceptions import ValidationError
+from django.core.exceptions import FieldDoesNotExist, ValidationError
 from django.db import models
 from django.utils.encoding import force_str
 from django.utils.translation import gettext_lazy as _
@@ -325,14 +325,14 @@ def clean(self):
         for field in self.claim_mapping.keys():
             try:
                 User._meta.get_field(field)
-            except models.FieldDoesNotExist:
+            except FieldDoesNotExist as exc:
                 raise ValidationError(
                     {
                         "claim_mapping": _(
-                            "Field {field} does not exist on the user model"
+                            "Field '{field}' does not exist on the user model"
                         ).format(field=field)
                     }
-                )
+                ) from exc
 
         if User.USERNAME_FIELD in self.claim_mapping:
             raise ValidationError(
diff --git a/tests/test_models.py b/tests/test_models.py
index 556fafd..7c3dadd 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -1,4 +1,6 @@
+from django.core.exceptions import ValidationError
 from django.test.utils import isolate_apps
+from django.utils.translation import gettext as _
 
 import pytest
 
@@ -53,3 +55,37 @@ def custom_oidc_db_prefix(cls):
 
     # Prefix taken from `mozilla_django_oidc_dv/settings.py`
     assert CustomConfig.get_cache_key() == "oidc:customconfig"
+
+
+def test_validate_claim_mapping_fields():
+    instance = OpenIDConnectConfig(
+        claim_mapping={
+            "bad_field_no_cookie": ["har"],
+        }
+    )
+
+    with pytest.raises(ValidationError) as exc_context:
+        instance.clean()
+
+    err_dict = exc_context.value.message_dict
+    assert "claim_mapping" in err_dict
+    error = _("Field '{field}' does not exist on the user model").format(
+        field="bad_field_no_cookie"
+    )
+    assert error in err_dict["claim_mapping"]
+
+
+def test_validate_username_field_not_in_claim_mapping():
+    instance = OpenIDConnectConfig(
+        claim_mapping={
+            "username": ["nope"],
+        }
+    )
+
+    with pytest.raises(ValidationError) as exc_context:
+        instance.clean()
+
+    err_dict = exc_context.value.message_dict
+    assert "claim_mapping" in err_dict
+    error = _("The username field may not be in the claim mapping")
+    assert error in err_dict["claim_mapping"]