diff --git a/pungi/phases/gather/__init__.py b/pungi/phases/gather/__init__.py
index 436d582f..8667b678 100644
--- a/pungi/phases/gather/__init__.py
+++ b/pungi/phases/gather/__init__.py
@@ -238,7 +238,7 @@ def reuse_old_gather_packages(compose, arch, variant, package_sets):
                     # The gather_lookaside_repos config allows setting multiple repourls
                     # using list, but `_update_config` always uses strings. Therefore we
                     # only try to filter out string_types.
-                    if isinstance(repourl, six.string_types):
+                    if not isinstance(repourl, six.string_types):
                         continue
                     if not repourl.startswith(compose.topdir):
                         per_arch_repos_to_compare[arch] = repourl
diff --git a/tests/test_gather_phase.py b/tests/test_gather_phase.py
index c9b2086d..bf831c19 100644
--- a/tests/test_gather_phase.py
+++ b/tests/test_gather_phase.py
@@ -1236,6 +1236,26 @@ class TestReuseOldGatherPackages(helpers.PungiTestCase):
         )
         self.assertEqual(result, None)
 
+    @mock.patch("pungi.phases.gather.load_old_gather_result")
+    @mock.patch("pungi.phases.gather.load_old_compose_config")
+    def test_reuse_update_gather_lookaside_repos_different_initial_repos_list(
+        self, load_old_compose_config, load_old_gather_result
+    ):
+        package_sets = self._prepare_package_sets(
+            load_old_gather_result, requires=[], provides=[]
+        )
+        compose = helpers.DummyCompose(self.topdir, {"gather_allow_reuse": True})
+        lookasides = compose.conf["gather_lookaside_repos"]
+        repos = ["http://localhost/real1.repo", "http://localhost/real2.repo"]
+        lookasides.append(("^Server$", {"x86_64": repos}))
+        load_old_compose_config.return_value = copy.deepcopy(compose.conf)
+
+        gather._update_config(compose, "Server", "x86_64", compose.topdir)
+        result = gather.reuse_old_gather_packages(
+            compose, "x86_64", compose.variants["Server"], package_sets
+        )
+        self.assertEqual(result, None)
+
     @mock.patch("pungi.phases.gather.load_old_gather_result")
     @mock.patch("pungi.phases.gather.load_old_compose_config")
     def test_reuse_no_old_file_cache(