diff --git a/scrapy/responsetypes.py b/scrapy/responsetypes.py
index 147fd2628..e60ca04dd 100644
--- a/scrapy/responsetypes.py
+++ b/scrapy/responsetypes.py
@@ -136,7 +136,7 @@ class ResponseTypes:
             mimetype, encoding = self.mimetypes.guess_type(filename)
             if encoding:
                 return (f"application/{encoding}".encode(),)
-            else:
+            elif mimetype:
                 return (mimetype.encode(),)
 
         return None
diff --git a/tests/test_responsetypes.py b/tests/test_responsetypes.py
index 52b0e2507..2d3ae93ce 100644
--- a/tests/test_responsetypes.py
+++ b/tests/test_responsetypes.py
@@ -90,6 +90,7 @@ class ResponseTypesTest(unittest.TestCase):
             ({'filename': 'file.pdf'}, Response),
             ({'url': 'http://www.example.com/item/file.pdf'}, Response),
             ({'body': b'Some plain text data\1\2 with tabs and\n null bytes\0'}, Response),
+            ({'filename': '/tmp/temp^'}, TextResponse),
         ]
         for source, cls in mappings:
             retcls = responsetypes.from_args(**source)
diff --git a/tox.ini b/tox.ini
index 86e1d78f8..d31ea5517 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,7 +17,7 @@ deps =
     #mitmproxy >= 5.3.0; python_version >= '3.9' and implementation_name != 'pypy'
     mitmproxy >= 4.0.4; python_version >= '3.7' and python_version < '3.9' and implementation_name != 'pypy'
     mitmproxy >= 4.0.4, < 5; python_version >= '3.6' and python_version < '3.7' and platform_system != 'Windows' and implementation_name != 'pypy'
-    git+https://github.com/scrapy/xtractmime.git@binary#egg=xtractmime
+    git+https://github.com/scrapy/xtractmime.git@main#egg=xtractmime
     # Extras
     botocore>=1.4.87
 passenv =
@@ -79,6 +79,7 @@ deps =
     Twisted[http2]==17.9.0
     w3lib==1.17.0
     zope.interface==4.1.3
+    git+https://github.com/scrapy/xtractmime.git@main#egg=xtractmime
     -rtests/requirements-py3.txt
 
     # mitmproxy 4.0.4+ requires upgrading some of the pinned dependencies