diff --git a/changelog.d/15814.misc b/changelog.d/15814.misc
new file mode 100644
index 000000000000..8e1107212f17
--- /dev/null
+++ b/changelog.d/15814.misc
@@ -0,0 +1 @@
+Fix harmless exceptions being printed when running the port DB script.
diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index 27fee3d9a934..a803ada8ad06 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -1369,6 +1369,9 @@ def main() -> None:
         sys.stderr.write("Database must use the 'psycopg2' connector.\n")
         sys.exit(3)
 
+    # Don't run the background tasks that get started by the data stores.
+    hs_config["run_background_tasks_on"] = "some_other_process"
+
     config = HomeServerConfig()
     config.parse_config_dict(hs_config, "", "")