diff --git a/src/scripting/thingdef_data.cpp b/src/scripting/thingdef_data.cpp
index b8cfd8d74..cc97b1a2d 100644
--- a/src/scripting/thingdef_data.cpp
+++ b/src/scripting/thingdef_data.cpp
@@ -354,7 +354,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF9, SHADOWAIMVERT, AActor, flags9),
 	DEFINE_FLAG(MF9, DECOUPLEDANIMATIONS, AActor, flags9),
 	DEFINE_FLAG(MF9, NOSECTORDAMAGE, AActor, flags9),
-	DEFINE_FLAG(MF9, ISPUFF, AActor, flags9), //[AA] was spawned by SpawnPuff
+	DEFINE_PROTECTED_FLAG(MF9, ISPUFF, AActor, flags9), //[AA] was spawned by SpawnPuff
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),
diff --git a/wadsrc/static/zscript/actors/actor.zs b/wadsrc/static/zscript/actors/actor.zs
index eebfbe329..cae1d161b 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -148,7 +148,7 @@ class Actor : Thinker native
 	native Actor Target;
 	native Actor Master;
 	native Actor Tracer;
-	native Actor DamageSource;
+	native readonly Actor DamageSource;
 	native Actor LastHeard;
 	native Actor LastEnemy;
 	native Actor LastLookActor;