diff --git a/extra/L-system/models/abop-4/abop-4.factor b/extra/L-system/models/abop-4/abop-4.factor
index 6b2688a478..71cf32d4d7 100644
--- a/extra/L-system/models/abop-4/abop-4.factor
+++ b/extra/L-system/models/abop-4/abop-4.factor
@@ -9,6 +9,8 @@ IN: L-system.models.abop-4
 
   L-parser-dialect >>commands
 
+  [ 18 >>angle ] >>turtle-values
+
   "c(12)&(20)N" >>axiom
 
   {