diff --git a/source/tools/monitor/unity/tsdb/foxTSDB.lua b/source/tools/monitor/unity/tsdb/foxTSDB.lua
index 536d13841705f3f6bcb4c51781f1c45622867f4d..69f2c5e57481b9d21b562d1809c2db2e6590bba8 100644
--- a/source/tools/monitor/unity/tsdb/foxTSDB.lua
+++ b/source/tools/monitor/unity/tsdb/foxTSDB.lua
@@ -202,9 +202,10 @@ function CfoxTSDB:curMove(us)
 end
 
 function CfoxTSDB:resize()
-    assert(self._man)
-    local ret = self.cffi.fox_read_resize(self._man)
-    assert(ret >= 0, string.format("resize bad ret: %d", ret))
+    if self._man then
+        local ret = self.cffi.fox_read_resize(self._man)
+        assert(ret >= 0, string.format("resize bad ret: %d", ret))
+    end
 end
 
 function CfoxTSDB:loadData(stop_us)