diff --git a/patroni/api.py b/patroni/api.py
index 36b950a1..ba37d5a0 100644
--- a/patroni/api.py
+++ b/patroni/api.py
@@ -215,7 +215,7 @@ class RestApiHandler(BaseHTTPRequestHandler):
                         status_code = 400
                         data = "PostgreSQL version should be in the first.major.minor format"
                         break
-                else:
+                elif k != 'with_pending_restart_flag':
                     status_code = 400
                     data = "Unknown filter for the scheduled restart: {0}".format(k)
                     break