diff --git a/tests/integration/postgres/conftest.py b/tests/integration/postgres/conftest.py
index 850260f..49155d1 100644
--- a/tests/integration/postgres/conftest.py
+++ b/tests/integration/postgres/conftest.py
@@ -36,7 +36,15 @@ def postgres_container() -> Iterator[PostgresContainer]:
 
 @pytest.fixture(scope="session")
 def postgres_url(postgres_container: PostgresContainer) -> str:
-    return postgres_container.get_connection_url()
+    """The container's URL, pinned to IPv4.
+
+    Testcontainers reports the host as `localhost`, which resolves to `::1`
+    before `127.0.0.1`. Docker publishes the mapped port on IPv4 only, and the
+    IPv6 SYN is dropped rather than refused, so asyncpg blocks on the first
+    address until its connect timeout instead of falling back to the second --
+    the connection does not fail, it hangs.
+    """
+    return postgres_container.get_connection_url().replace("@localhost:", "@127.0.0.1:")
 
 
 @pytest.fixture(scope="session")