diff --git a/codex/cli.py b/codex/cli.py
index 33ab2c8..28130b7 100644
--- a/codex/cli.py
+++ b/codex/cli.py
@@ -84,10 +84,10 @@ def search_paper(
         rows = conn.execute(
             """
             SELECT id, title, year,
-                   abstract_emb <-> %(emb)s AS distance
+                   abstract_emb <-> %(emb)s::vector AS distance
             FROM   papers
             WHERE  abstract_emb IS NOT NULL
-            ORDER  BY abstract_emb <-> %(emb)s
+            ORDER  BY abstract_emb <-> %(emb)s::vector
             LIMIT  %(limit)s
             """,
             {"emb": emb, "limit": limit},
diff --git a/tests/cli/test_cli.py b/tests/cli/test_cli.py
index 4d15713..9561191 100644
--- a/tests/cli/test_cli.py
+++ b/tests/cli/test_cli.py
@@ -106,6 +106,13 @@ class TestSearch:
             assert "Test Paper" in result.stdout
             assert "0.123" in result.stdout
 
+            # Regression guard (DQ-4): the pgvector `<->` operator requires the
+            # query embedding cast to ::vector. Without it, real Postgres raises
+            # "operator does not exist: vector <-> double precision[]". Mocked DBs
+            # don't catch the type error, so assert the cast is in the SQL.
+            executed_sql = mock_conn.execute.call_args_list[0][0][0]
+            assert "<->" in executed_sql and "::vector" in executed_sql
+
     def test_search_formula_command(self) -> None:
         """Test `search formula` command with mocked DB."""
         with patch("codex.db.get_conn") as mock_get_conn: