diff --git a/scrapy/pipelines/files.py b/scrapy/pipelines/files.py
index 72e210469..d5ed3121d 100644
--- a/scrapy/pipelines/files.py
+++ b/scrapy/pipelines/files.py
@@ -222,8 +222,8 @@ class GCSFilesStore:
                 return {'checksum': checksum, 'last_modified': last_modified}
             else:
                 return {}
-
-        return threads.deferToThread(self.bucket.get_blob, path).addCallback(_onsuccess)
+        blob_path = self._get_blob_path(path)
+        return threads.deferToThread(self.bucket.get_blob, blob_path).addCallback(_onsuccess)
 
     def _get_content_type(self, headers):
         if headers and 'Content-Type' in headers:
@@ -231,8 +231,12 @@ class GCSFilesStore:
         else:
             return 'application/octet-stream'
 
+    def _get_blob_path(self, path):
+        return self.prefix + path
+
     def persist_file(self, path, buf, info, meta=None, headers=None):
-        blob = self.bucket.blob(self.prefix + path)
+        blob_path = self._get_blob_path(path)
+        blob = self.bucket.blob(blob_path)
         blob.cache_control = self.CACHE_CONTROL
         blob.metadata = {k: str(v) for k, v in (meta or {}).items()}
         return threads.deferToThread(
diff --git a/tests/test_pipeline_files.py b/tests/test_pipeline_files.py
index 4e1b90787..0ff2045ed 100644
--- a/tests/test_pipeline_files.py
+++ b/tests/test_pipeline_files.py
@@ -525,6 +525,29 @@ class TestGCSFilesStore(unittest.TestCase):
         self.assertEqual(blob.content_type, 'application/octet-stream')
         self.assertIn(expected_policy, acl)
 
+    @defer.inlineCallbacks
+    def test_blob_path_consistency(self):
+        """Test to make sure that paths used to store files is the same as the one used to get
+        already uploaded files.
+        """
+        assert_gcs_environ()
+        try:
+            import google.cloud.storage # noqa
+        except ModuleNotFoundError:
+            raise unittest.SkipTest("google-cloud-storage is not installed")
+        else:
+            with mock.patch('google.cloud.storage') as _:
+                with mock.patch('scrapy.pipelines.files.time') as _:
+                    uri = 'gs://my_bucket/my_prefix/'
+                    store = GCSFilesStore(uri)
+                    store.bucket = mock.Mock()
+                    path = 'full/my_data.txt'
+                    yield store.persist_file(path, mock.Mock(), info=None, meta=None, headers=None)
+                    yield store.stat_file(path, info=None)
+                    expected_blob_path = store.prefix + path
+                    store.bucket.blob.assert_called_with(expected_blob_path)
+                    store.bucket.get_blob.assert_called_with(expected_blob_path)
+
 
 class TestFTPFileStore(unittest.TestCase):
     @defer.inlineCallbacks
diff --git a/tox.ini b/tox.ini
index db151f215..6951b6d16 100644
--- a/tox.ini
+++ b/tox.ini
@@ -12,10 +12,11 @@ deps =
     -rtests/requirements.txt
     # mitmproxy does not support PyPy
     # mitmproxy does not support Windows when running Python < 3.7
-    # Python 3.9+ requires https://github.com/mitmproxy/mitmproxy/commit/8e5e43de24c9bc93092b63efc67fbec029a9e7fe
+    # Python 3.9+ requires mitmproxy >= 5.3.0
     # mitmproxy >= 5.3.0 requires h2 >= 4.0, Twisted 21.2 requires h2 < 4.0
     #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'
+    # The tests hang with mitmproxy 8.0.0: https://github.com/scrapy/scrapy/issues/5454
+    mitmproxy >= 4.0.4, < 8; 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'
     # newer markupsafe is incompatible with deps of old mitmproxy (which we get on Python 3.7 and lower)
     markupsafe < 2.1.0; python_version >= '3.6' and python_version < '3.8' and implementation_name != 'pypy'
@@ -125,13 +126,14 @@ setenv =
 deps =
     {[testenv]deps}
     boto
+    google-cloud-storage
+    # Twisted[http2] currently forces old mitmproxy because of h2 version
+    # restrictions in their deps, so we need to pin old markupsafe here too.
+    markupsafe < 2.1.0
     reppy
     robotexclusionrulesparser
     Pillow>=4.0.0
     Twisted[http2]>=17.9.0
-    # Twisted[http2] currently forces old mitmproxy because of h2 version restrictions in their deps,
-    # so we need to pin old markupsafe here too
-    markupsafe < 2.1.0
 
 [testenv:asyncio]
 commands =