diff --git a/tests/fixtures.py b/tests/fixtures.py
index e2f90f09..a4a96919 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -268,6 +268,9 @@ def make_app_client(
                 "default_page_size": 50,
                 "max_returned_rows": max_returned_rows or 100,
                 "sql_time_limit_ms": sql_time_limit_ms or 200,
+                # Default is 3 but this results in "too many open files"
+                # errors when running the full test suite:
+                "num_sql_threads": 1,
             }
         )
         ds = Datasette(
diff --git a/tests/test_api.py b/tests/test_api.py
index 1a54edec..322a0001 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -1320,7 +1320,7 @@ def test_config_json(app_client):
         "suggest_facets": True,
         "default_cache_ttl": 5,
         "default_cache_ttl_hashed": 365 * 24 * 60 * 60,
-        "num_sql_threads": 3,
+        "num_sql_threads": 1,
         "cache_size_kb": 0,
         "allow_csv_stream": True,
         "max_csv_mb": 100,