diff --git a/openpype/modules/sync_server/sync_server_module.py b/openpype/modules/sync_server/sync_server_module.py
index 596aeb8b39..3744a21b43 100644
--- a/openpype/modules/sync_server/sync_server_module.py
+++ b/openpype/modules/sync_server/sync_server_module.py
@@ -300,13 +300,13 @@ class SyncServerModule(OpenPypeModule, ITrayModule):
         Returns:
             (dict): {'site': [alternative sites]...}
         """
-        alt_site_pairs = defaultdict(list)
+        alt_site_pairs = defaultdict(set)
         for site_name, site_info in conf_sites.items():
             alt_sites = set(site_info.get("alternative_sites", []))
-            alt_site_pairs[site_name].extend(alt_sites)
+            alt_site_pairs[site_name].update(alt_sites)
 
             for alt_site in alt_sites:
-                alt_site_pairs[alt_site].append(site_name)
+                alt_site_pairs[alt_site].add(site_name)
 
         for site_name, alt_sites in alt_site_pairs.items():
             sites_queue = deque(alt_sites)
@@ -323,7 +323,7 @@ class SyncServerModule(OpenPypeModule, ITrayModule):
                             alt_alt_site != site_name
                             and alt_alt_site not in alt_sites
                     ):
-                        alt_sites.append(alt_alt_site)
+                        alt_sites.add(alt_alt_site)
                         sites_queue.append(alt_alt_site)
 
         return alt_site_pairs
diff --git a/tests/unit/openpype/modules/sync_server/test_module_api.py b/tests/unit/openpype/modules/sync_server/test_module_api.py
index 14613604dd..b7d3383c0b 100644
--- a/tests/unit/openpype/modules/sync_server/test_module_api.py
+++ b/tests/unit/openpype/modules/sync_server/test_module_api.py
@@ -37,9 +37,9 @@ class TestModuleApi(ModuleUnitTest):
                       "studio2": {"alternative_sites": ["studio"]}}
 
         ret = setup_sync_server_module._get_alt_site_pairs(conf_sites)
-        expected = {"SFTP": ["studio", "studio2"],
-                    "studio": ["SFTP", "studio2"],
-                    "studio2": ["studio", "SFTP"]}
+        expected = {"SFTP": {"studio", "studio2"},
+                    "studio": {"SFTP", "studio2"},
+                    "studio2": {"studio", "SFTP"}}
         assert ret == expected, "Not matching result"