diff --git a/changelog_entry.yaml b/changelog_entry.yaml
index e69de29b..c606c93c 100644
--- a/changelog_entry.yaml
+++ b/changelog_entry.yaml
@@ -0,0 +1,5 @@
+- bump: patch
+  changes:
+    fixed:
+    - Fail closed when authentication is enabled but Auth0 configuration is
+      incomplete.
diff --git a/policyengine_household_api/decorators/auth.py b/policyengine_household_api/decorators/auth.py
index a675b45f..88f95d62 100644
--- a/policyengine_household_api/decorators/auth.py
+++ b/policyengine_household_api/decorators/auth.py
@@ -10,7 +10,7 @@
 from authlib.integrations.flask_oauth2 import ResourceProtector
 from authlib.oauth2.rfc6750 import BearerTokenValidator
 from ..auth.validation import Auth0JWTBearerTokenValidator
-from ..utils.config_loader import get_config, get_config_value
+from ..utils.config_loader import get_config_value
 
 
 class StaticBearerToken:
@@ -120,10 +120,15 @@ def _setup_authentication(self) -> None:
                 resource_protector.register_token_validator(validator)
                 self._decorator = resource_protector
             else:
-                # Auth was requested but configuration is missing
-                print("Warning: Auth enabled but Auth0 configuration missing")
-                self._auth_enabled = False
-                self._decorator = NoOpDecorator()
+                missing = []
+                if not auth0_address:
+                    missing.append("auth.auth0.address")
+                if not auth0_audience:
+                    missing.append("auth.auth0.audience")
+                raise RuntimeError(
+                    "Authentication is enabled but required Auth0 "
+                    f"configuration is missing: {', '.join(missing)}"
+                )
         else:
             # Authentication is disabled
             self._decorator = NoOpDecorator()
diff --git a/tests/unit/decorators/test_auth.py b/tests/unit/decorators/test_auth.py
index a2089d43..0d549585 100644
--- a/tests/unit/decorators/test_auth.py
+++ b/tests/unit/decorators/test_auth.py
@@ -3,6 +3,7 @@
 """
 
 from unittest.mock import Mock
+import pytest
 from policyengine_household_api.decorators.auth import (
     NoOpDecorator,
     ConditionalAuthDecorator,
@@ -122,26 +123,26 @@ def test__given_auth_enabled_with_valid_config__auth0_is_configured(
         auth_enabled_environment.assert_any_call("auth.auth0.address", "")
         auth_enabled_environment.assert_any_call("auth.auth0.audience", "")
 
-    def test__given_auth_enabled_missing_config__falls_back_to_noop(
+    def test__given_auth_enabled_missing_config__raises_configuration_error(
         self,
         auth_enabled_missing_config_environment,
         mock_resource_protector,
         mock_auth0_validator,
     ):
-        """Test fallback to NoOp when auth is enabled but config is missing."""
+        """Test auth fails closed when enabled but config is missing."""
         mock_protector_class, _ = mock_resource_protector
         mock_validator_class, _ = mock_auth0_validator
 
-        decorator = ConditionalAuthDecorator()
+        with pytest.raises(
+            RuntimeError,
+            match="Authentication is enabled but required Auth0 configuration is missing",
+        ):
+            ConditionalAuthDecorator()
 
         # Verify Auth0 components were not created
         mock_validator_class.assert_not_called()
         mock_protector_class.assert_not_called()
 
-        # Verify we get a NoOpDecorator
-        assert isinstance(decorator.get_decorator(), NoOpDecorator)
-        assert decorator.is_enabled is False
-
         # Verify configuration was checked
         auth_enabled_missing_config_environment.assert_any_call(
             "auth.enabled", False