diff --git a/python/tests/test_collection.py b/python/tests/test_collection.py
index 7eba2e2..b03d1e3 100644
--- a/python/tests/test_collection.py
+++ b/python/tests/test_collection.py
@@ -13,6 +13,8 @@
 # limitations under the License.
 from __future__ import annotations
 
+from unittest.mock import MagicMock
+
 import pytest
 import zvec
 from zvec import (
@@ -907,6 +909,17 @@ class TestCollectionQuery:
         assert len(doc.field_names()) == 2
         assert set(doc.field_names()) == {"id", "name"}
 
+    @pytest.mark.parametrize("topk", [0, -1, None, True])
+    def test_collection_query_rejects_invalid_topk(self, topk):
+        collection = Collection.__new__(Collection)
+        collection._querier = MagicMock()
+        collection._obj = MagicMock()
+
+        with pytest.raises(ValueError, match="topk must be a positive integer"):
+            collection.query(Query(field_name="dense", vector=[0.1]), topk=topk)
+
+        collection._querier.execute.assert_not_called()
+
     def test_collection_query_with_topk(
         self, collection_with_multiple_docs: Collection
     ):
diff --git a/python/zvec/model/collection.py b/python/zvec/model/collection.py
index 6663a1b..a002d0d 100644
--- a/python/zvec/model/collection.py
+++ b/python/zvec/model/collection.py
@@ -423,6 +423,7 @@ class Collection:
             ...     output_fields=["title", "url"]
             ... )
         """
+        _require_positive_integer(topk, "topk")
         if vectors is not None:
             warnings.warn(
                 "The 'vectors' parameter is deprecated and will be removed in a future version. "