diff --git a/src/playsim/actor.h b/src/playsim/actor.h
index b0f8a1da7..061909b5b 100644
--- a/src/playsim/actor.h
+++ b/src/playsim/actor.h
@@ -734,7 +734,7 @@ public:
 const double MinVel = EQUAL_EPSILON;
 
 // Map Object definition.
-class AActor : public DThinker
+class AActor final : public DThinker
 {
 	DECLARE_CLASS_WITH_META (AActor, DThinker, PClassActor)
 	HAS_OBJECT_POINTERS