1 files changed, 3 insertions, 1 deletions
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 3e59805baa..37321f9133 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -130,7 +130,7 @@ def start_reactor(
     appname: str,
     soft_file_limit: int,
     gc_thresholds: Optional[Tuple[int, int, int]],
-    pid_file: str,
+    pid_file: Optional[str],
     daemonize: bool,
     print_pidfile: bool,
     logger: logging.Logger,
@@ -171,6 +171,8 @@ def start_reactor(
     # appearing to go backwards.
     with PreserveLoggingContext():
         if daemonize:
+            assert pid_file is not None
+
             if print_pidfile:
                 print(pid_file)