diff --git a/src/playsim/actor.h b/src/playsim/actor.h
index 8c1a32d53..3aaca5724 100644
--- a/src/playsim/actor.h
+++ b/src/playsim/actor.h
@@ -414,7 +414,7 @@ enum ActorFlag8
 	MF8_STOPRAILS		= 0x00000200,	// [MC] Prevent rails from going further if an actor has this flag.
 	MF8_ABSVIEWANGLES	= 0x00000400,	// [MC] By default view angle/pitch/roll is an offset. This will make it absolute instead.
 	MF8_FALLDAMAGE		= 0x00000800,	// Monster will take fall damage regardless of map settings.
-	MF8_THRUBITS		= 0x00008000,	// [MC] Enable ThruBits property
+	MF8_ALLOWTHRUBITS		= 0x00008000,	// [MC] Enable ThruBits property
 };
 
 // --- mobj.renderflags ---
diff --git a/src/playsim/p_map.cpp b/src/playsim/p_map.cpp
index e051b3a52..b976fac5b 100644
--- a/src/playsim/p_map.cpp
+++ b/src/playsim/p_map.cpp
@@ -450,7 +450,7 @@ bool	P_TeleportMove(AActor* thing, const DVector3 &pos, bool telefrag, bool modi
 		if ((th->flags2 | tmf.thing->flags2) & MF2_THRUACTORS)
 			continue;
 
-		if (((th->flags8 | tmf.thing->flags8) & MF8_THRUBITS) && th->ThruBits & tmf.thing->ThruBits)
+		if ((th->ThruBits & tmf.thing->ThruBits) && ((th->flags8 | tmf.thing->flags8) & MF8_ALLOWTHRUBITS))
 			continue;
 
 		double blockdist = th->radius + tmf.thing->radius;
@@ -1304,7 +1304,7 @@ bool PIT_CheckThing(FMultiBlockThingsIterator &it, FMultiBlockThingsIterator::Ch
 	if ((thing->flags2 | tm.thing->flags2) & MF2_THRUACTORS)
 		return true;
 
-	if (((thing->flags8 | tm.thing->flags8) & MF8_THRUBITS) && thing->ThruBits & tm.thing->ThruBits)
+	if ((thing->ThruBits & tm.thing->ThruBits) && ((thing->flags8 | tm.thing->flags8) & MF8_ALLOWTHRUBITS))
 		return true;
 
 	if (!((thing->flags & (MF_SOLID | MF_SPECIAL | MF_SHOOTABLE)) || thing->flags6 & MF6_TOUCHY))
@@ -2000,7 +2000,7 @@ int P_TestMobjZ(AActor *actor, bool quick, AActor **pOnmobj)
 		{
 			continue;
 		}
-		if (((actor->flags8 | thing->flags8) & MF8_THRUBITS) && actor->ThruBits & thing->ThruBits)
+		if ((actor->ThruBits & thing->ThruBits) && ((actor->flags8 | thing->flags8) & MF8_ALLOWTHRUBITS))
 		{
 			continue;
 		}
@@ -4509,7 +4509,7 @@ AActor *P_LineAttack(AActor *t1, DAngle angle, double distance,
 		if (tempuff != NULL)
 		{
 			TData.PuffSpecies = tempuff->GetSpecies();
-			TData.UseThruBits = tempuff->flags8 & MF8_THRUBITS;
+			TData.UseThruBits = tempuff->flags8 & MF8_ALLOWTHRUBITS;
 			TData.ThruBits = tempuff->ThruBits;
 			tempuff->Destroy();
 		}
@@ -5269,7 +5269,7 @@ void P_RailAttack(FRailParams *p)
 	{
 		rail_data.ThruBits = thepuff->ThruBits;
 		if (rail_data.UseThruBits)
-			rail_data.UseThruBits = (thepuff->flags8 & MF8_THRUBITS);
+			rail_data.UseThruBits = !!(thepuff->flags8 & MF8_ALLOWTHRUBITS);
 	}
 
 	Trace(start, source->Sector, vec, p->distance, MF_SHOOTABLE, ML_BLOCKEVERYTHING, source, trace,	flags, ProcessRailHit, &rail_data);
diff --git a/src/scripting/thingdef_data.cpp b/src/scripting/thingdef_data.cpp
index 0749f5a9c..1f100af1f 100644
--- a/src/scripting/thingdef_data.cpp
+++ b/src/scripting/thingdef_data.cpp
@@ -327,7 +327,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF8, STOPRAILS, AActor, flags8),
 	DEFINE_FLAG(MF8, FALLDAMAGE, AActor, flags8),
 	DEFINE_FLAG(MF8, ABSVIEWANGLES, AActor, flags8),
-	DEFINE_FLAG(MF8, THRUBITS, AActor, flags8),
+	DEFINE_FLAG(MF8, ALLOWTHRUBITS, AActor, flags8),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),