diff --git a/test_runner/regress/test_pg_regress.py b/test_runner/regress/test_pg_regress.py
index 54b493ec70..d5b5ac3f75 100644
--- a/test_runner/regress/test_pg_regress.py
+++ b/test_runner/regress/test_pg_regress.py
@@ -117,7 +117,7 @@ def post_checks(env: NeonEnv, test_output_dir: Path, db_name: str, endpoint: End
 
 # Run the main PostgreSQL regression tests, in src/test/regress.
 #
-@pytest.mark.timeout(600)
+@pytest.mark.timeout(900)  # Contains many sub-tests, is slow in debug builds
 @pytest.mark.parametrize("shard_count", [None, 4])
 def test_pg_regress(
     neon_env_builder: NeonEnvBuilder,
@@ -186,6 +186,7 @@ def test_pg_regress(
 
 # Run the PostgreSQL "isolation" tests, in src/test/isolation.
 #
+@pytest.mark.timeout(600)  # Contains many sub-tests, is slow in debug builds
 @pytest.mark.parametrize("shard_count", [None, 4])
 def test_isolation(
     neon_env_builder: NeonEnvBuilder,