diff --git a/changelog.d/10499.bugfix b/changelog.d/10499.bugfix
new file mode 100644
index 0000000000..6487af6c96
--- /dev/null
+++ b/changelog.d/10499.bugfix
@@ -0,0 +1 @@
+Fix a bug which caused an explicit assignment of power-level 0 to a user to be misinterpreted in rare circumstances.
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 0fa7ffc99f..4c92e9a2d4 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -692,7 +692,7 @@ def get_user_power_level(user_id: str, auth_events: StateMap[EventBase]) -> int:
     power_level_event = get_power_level_event(auth_events)
     if power_level_event:
         level = power_level_event.content.get("users", {}).get(user_id)
-        if not level:
+        if level is None:
             level = power_level_event.content.get("users_default", 0)
 
         if level is None: