diff --git a/tests/functional_tests.py b/tests/functional_tests.py
index 6bdafd3..714a5c4 100644
--- a/tests/functional_tests.py
+++ b/tests/functional_tests.py
@@ -1,5 +1,6 @@
 """Test page requests."""
 import re
+from unittest.mock import patch
 
 
 def test_page_that_exists(client):
@@ -41,6 +42,24 @@ def test_internal_server_error_serves_error_page(client):
     assert b'bss@incorporeal.org' in response.data
 
 
+def test_oserror_is_500(client, app):
+    """Test that an OSError raises as a 500."""
+    with app.test_request_context():
+        with patch('flask.current_app.open_instance_resource', side_effect=OSError):
+            response = client.get('/')
+            assert response.status_code == 500
+            assert b'INTERNAL SERVER ERROR' in response.data
+
+
+def test_unsupported_file_type_is_500(client, app):
+    """Test a coding condition mishap raises as a 500."""
+    with app.test_request_context():
+        with patch('incorporealcms.pages.request_path_to_instance_resource_path', return_value=('foo', 'bar')):
+            response = client.get('/')
+            assert response.status_code == 500
+            assert b'INTERNAL SERVER ERROR' in response.data
+
+
 def test_weird_paths_do_not_get_served(client):
     """Test that we clean up requests as desired."""
     response = client.get('/../../')