diff --git a/panda/src/express/clockObject.cxx b/panda/src/express/clockObject.cxx
index 712d8933d3..1bad0741b7 100644
--- a/panda/src/express/clockObject.cxx
+++ b/panda/src/express/clockObject.cxx
@@ -22,6 +22,7 @@ ClockObject() {
   _actual_frame_time = 0.0;
   _reported_frame_time = 0.0;
   _dt = 0.0;
+  _max_dt = -1.0;
 }
 
 ////////////////////////////////////////////////////////////////////