diff --git a/stdpopsim/slim_engine.py b/stdpopsim/slim_engine.py
index 1fa867d2d..5c1a114ce 100644
--- a/stdpopsim/slim_engine.py
+++ b/stdpopsim/slim_engine.py
@@ -216,7 +216,7 @@
      * start of the next tick.
      */
     sb = community.allScriptBlocks;
-    sb[sb.type == "late"].active = F;
+    sb[sb.type == "late"].active = 0;
 
     /*
      * 2. The late events below were run in the save() tick,