diff --git a/examples/simple.py b/examples/simple.py
index 6b0830d..1ab9c65 100644
--- a/examples/simple.py
+++ b/examples/simple.py
@@ -680,6 +680,12 @@ def forbidden(req):
     raise HTTPException(state.HTTP_FORBIDDEN)
 
 
+@app.route('/not-modified')
+def not_modified_result(_):
+    """Test for raise not NotModifiedResponse"""
+    raise HTTPException(NotModifiedResponse(etag="012"))
+
+
 @app.route('/not-implemented')
 def not_implemented(req):
     """Test not implemented exception"""
diff --git a/poorwsgi/results.py b/poorwsgi/results.py
index cfecdbc..0c526e6 100644
--- a/poorwsgi/results.py
+++ b/poorwsgi/results.py
@@ -347,7 +347,7 @@ def method_not_allowed(req, error=None):
 # enddef
 
 
-def not_implemented(req, code=None, error=None):
+def not_implemented(req, code: int | None = None, error=None):
     """ 501 Not Implemented server error handler. """
     if error:
         log.error("501 - Not Implemented: %s", error)
@@ -372,7 +372,7 @@ def not_implemented(req, code=None, error=None):
         content += (
             "  <p>Your reqeuest <code>%s</code> returned not implemented\n"
             "   status code <code>%s</code>.</p>\n" % (req.uri, code))
-        log.error('Your reqeuest %s returned not implemented status code %d',
+        log.error('Your reqeuest %s returned not implemented status code %s',
                   req.uri, code)
     else:
         content += (
diff --git a/tests/test_responses.py b/tests/test_responses.py
index eab32cf..0c0b71b 100644
--- a/tests/test_responses.py
+++ b/tests/test_responses.py
@@ -564,6 +564,10 @@ def test_date_datetime(self):
                 date=datetime.fromtimestamp(0, timezone.utc))
         assert res.headers.get('Date') == "Thu, 01 Jan 1970 00:00:00 GMT"
 
+    def test_etag_only(self):
+        res = NotModifiedResponse(etag='W/"cd04a47544"')
+        assert res.headers.get("ETag") == 'W/"cd04a47544"'
+
     def test_date_empty_string(self):
         res = NotModifiedResponse(date="")
         assert res.headers.get('Date') is None
diff --git a/tests_integrity/test_simple.py b/tests_integrity/test_simple.py
index ae2ab9a..b72da9a 100644
--- a/tests_integrity/test_simple.py
+++ b/tests_integrity/test_simple.py
@@ -2,10 +2,10 @@
 from os import environ
 from os.path import dirname, join, pardir
 
-from requests import Session
 from pytest import fixture
+from requests import Session
 
-from . support import start_server, check_url
+from .support import check_url, start_server
 
 # pylint: disable=inconsistent-return-statements
 # pylint: disable=missing-function-docstring
@@ -55,6 +55,9 @@ def test_static_not_modified(self, url):
         check_url(url+"/test/static", status_code=304,
                   headers={'ETag': res.headers.get('ETag')})
 
+    def test_exception_not_modified(self, url):
+        check_url(url+"/not-modified", status_code=304)
+
     def test_variable_int(self, url):
         check_url(url+"/test/123")