diff --git a/optimade/server/entry_collections.py b/optimade/server/entry_collections.py
index 622884a79..f7dde4487 100644
--- a/optimade/server/entry_collections.py
+++ b/optimade/server/entry_collections.py
@@ -15,12 +15,12 @@
 from .query_params import EntryListingQueryParams, SingleEntryQueryParams
 
 try:
-    ci_force_mongo = bool(int(os.environ.get("OPTIMADE_CI_FORCE_MONGO", 0)))
+    CI_FORCE_MONGO = bool(int(os.environ.get("OPTIMADE_CI_FORCE_MONGO", 0)))
 except (TypeError, ValueError):  # pragma: no cover
-    ci_force_mongo = False
+    CI_FORCE_MONGO = False
 
 
-if CONFIG.use_real_mongo or ci_force_mongo:
+if CONFIG.use_real_mongo or CI_FORCE_MONGO:
     from pymongo import MongoClient
 
     client = MongoClient(CONFIG.mongo_uri)
diff --git a/tests/server/test_query_params.py b/tests/server/test_query_params.py
index 016cc048c..67b4823dc 100644
--- a/tests/server/test_query_params.py
+++ b/tests/server/test_query_params.py
@@ -4,9 +4,20 @@
 
 from optimade.server.config import CONFIG
 from optimade.server import mappers
+from optimade.server.entry_collections import CI_FORCE_MONGO
 
 from .utils import SetClient
 
+MONGOMOCK_OLD = False
+MONGOMOCK_MSG = ""
+if not CI_FORCE_MONGO and not CONFIG.use_real_mongo:
+    import mongomock
+
+    MONGOMOCK_OLD = tuple(
+        int(val) for val in mongomock.__version__.split(".")[0:3]
+    ) <= (3, 19, 0)
+    MONGOMOCK_MSG = f"mongomock version {mongomock.__version__}<=3.19.0 is too old for this test, skipping..."
+
 
 class IncludeTests(SetClient, unittest.TestCase):
     """Make sure `include` is handled correctly
@@ -394,12 +405,13 @@ def test_list_length(self):
         # expected_ids = []
         # self._check_response(request, expected_ids, len(expected_ids))
 
+    @unittest.skipIf(MONGOMOCK_OLD, MONGOMOCK_MSG)
     def test_list_has_only(self):
         """ Test HAS ONLY query on elements.
 
-        This test fails with mongomock<=3.1.9 when $size is 1, but works with a real mongo.
+        This test fails with mongomock<=3.19.0 when $size is 1, but works with a real mongo.
 
-        TODO: this text should be removed once mongomock>3.1.9 has been released, which should
+        TODO: this text and skip condition should be removed once mongomock>3.19.0 has been released, which should
         contain the bugfix for this: https://github.com/mongomock/mongomock/pull/597.
 
         """