diff --git a/src/p_map.cpp b/src/p_map.cpp
index 7f559fff4..55e90dcf6 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -3423,38 +3423,36 @@ fixed_t P_AimLineAttack (AActor *t1, angle_t angle, fixed_t distance, AActor **p
 //
 //==========================================================================
 
-static bool CheckForGhost (FTraceResults &res)
+static ETraceStatus CheckForGhost (FTraceResults &res, void *userdata)
 {
 	if (res.HitType != TRACE_HitActor)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// check for physical attacks on a ghost
 	if (res.Actor->flags3 & MF3_GHOST || res.Actor->flags4 & MF4_SPECTRAL)
 	{
-		res.HitType = TRACE_HitNone;
-		return true;
+		return TRACE_Skip;
 	}
 
-	return false;
+	return TRACE_Stop;
 }
 
-static bool CheckForSpectral (FTraceResults &res)
+static ETraceStatus CheckForSpectral (FTraceResults &res, void *userdata)
 {
 	if (res.HitType != TRACE_HitActor)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// check for physical attacks on spectrals
 	if (res.Actor->flags4 & MF4_SPECTRAL)
 	{
-		res.HitType = TRACE_HitNone;
-		return true;
+		return TRACE_Skip;
 	}
 
-	return false;
+	return TRACE_Stop;
 }
 
 //==========================================================================
@@ -3886,17 +3884,17 @@ struct SRailHit
 };
 static TArray<SRailHit> RailHits (16);
 
-static bool ProcessRailHit (FTraceResults &res)
+static ETraceStatus ProcessRailHit (FTraceResults &res, void *userdata)
 {
 	if (res.HitType != TRACE_HitActor)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// Invulnerable things completely block the shot
 	if (res.Actor->flags2 & MF2_INVULNERABLE)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// Save this thing for damaging later, and continue the trace
@@ -3905,7 +3903,7 @@ static bool ProcessRailHit (FTraceResults &res)
 	newhit.Distance = res.Distance - 10*FRACUNIT;	// put blood in front
 	RailHits.Push (newhit);
 
-	return true;
+	return TRACE_Continue;
 }
 
 //==========================================================================
@@ -3914,17 +3912,17 @@ static bool ProcessRailHit (FTraceResults &res)
 //
 //==========================================================================
 
-static bool ProcessNoPierceRailHit (FTraceResults &res)
+static ETraceStatus ProcessNoPierceRailHit (FTraceResults &res, void *userdata)
 {
 	if (res.HitType != TRACE_HitActor)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// Invulnerable things completely block the shot
 	if (res.Actor->flags2 & MF2_INVULNERABLE)
 	{
-		return false;
+		return TRACE_Stop;
 	}
 
 	// Only process the first hit
@@ -3933,7 +3931,7 @@ static bool ProcessNoPierceRailHit (FTraceResults &res)
 	newhit.Distance = res.Distance - 10*FRACUNIT;	// put blood in front
 	RailHits.Push (newhit);
 
-	return false;
+	return TRACE_Stop;
 }
 
 //==========================================================================
diff --git a/src/p_trace.cpp b/src/p_trace.cpp
index 93c347d9f..d1b9f63ac 100644
--- a/src/p_trace.cpp
+++ b/src/p_trace.cpp
@@ -48,7 +48,8 @@ struct FTraceInfo
 	sector_t *CurSector;
 	fixed_t MaxDist;
 	fixed_t EnterDist;
-	bool (*TraceCallback)(FTraceResults &res);
+	ETraceStatus (*TraceCallback)(FTraceResults &res, void *data);
+	void *TraceCallbackData;
 	DWORD TraceFlags;
 	int inshootthrough;
 
@@ -71,7 +72,7 @@ bool Trace (fixed_t x, fixed_t y, fixed_t z, sector_t *sector,
 			fixed_t vx, fixed_t vy, fixed_t vz, fixed_t maxDist,
 			DWORD actorMask, DWORD wallMask, AActor *ignore,
 			FTraceResults &res,
-			DWORD flags, bool (*callback)(FTraceResults &res))
+			DWORD flags, ETraceStatus (*callback)(FTraceResults &res, void *), void *callbackdata)
 {
 	int ptflags;
 	FTraceInfo inf;
@@ -91,6 +92,7 @@ bool Trace (fixed_t x, fixed_t y, fixed_t z, sector_t *sector,
 	inf.MaxDist = maxDist;
 	inf.EnterDist = 0;
 	inf.TraceCallback = callback;
+	inf.TraceCallbackData = callbackdata;
 	inf.TraceFlags = flags;
 	inf.Results = &res;
 	inf.inshootthrough = true;
@@ -506,7 +508,13 @@ cont:
 
 			if (TraceCallback != NULL)
 			{
-				if (!TraceCallback (*Results)) return false;
+				switch (TraceCallback(*Results, TraceCallbackData))
+				{
+				case TRACE_Stop:	return false;
+				case TRACE_Abort:	Results->HitType = TRACE_HitNone; return false;
+				case TRACE_Skip:	Results->HitType = TRACE_HitNone; break;
+				default:			break;
+				}
 			}
 			else
 			{
@@ -515,8 +523,7 @@ cont:
 		}
 
 		// Encountered an actor
-		if (!(in->d.thing->flags & ActorMask) ||
-			in->d.thing == IgnoreThis)
+		if (!(in->d.thing->flags & ActorMask) || in->d.thing == IgnoreThis)
 		{
 			continue;
 		}
@@ -583,13 +590,19 @@ cont:
 			// the trace hit a 3D-floor before the thing.
 			// Calculate an intersection and abort.
 			Results->Sector = &sectors[CurSector->sectornum];
-			if (!CheckSectorPlane(CurSector, Results->HitType==TRACE_HitFloor))
+			if (!CheckSectorPlane(CurSector, Results->HitType == TRACE_HitFloor))
 			{
-				Results->HitType=TRACE_HitNone;
+				Results->HitType = TRACE_HitNone;
 			}
 			if (TraceCallback != NULL)
 			{
-				return TraceCallback (*Results);
+				switch (TraceCallback(*Results, TraceCallbackData))
+				{
+				case TRACE_Continue: return true;
+				case TRACE_Stop:	 return false;
+				case TRACE_Abort:	 Results->HitType = TRACE_HitNone; return false;
+				case TRACE_Skip:	 Results->HitType = TRACE_HitNone; return true;
+				}
 			}
 			else
 			{
@@ -608,7 +621,13 @@ cont1:
 
 		if (TraceCallback != NULL)
 		{
-			if (!TraceCallback (*Results)) return false;
+			switch (TraceCallback(*Results, TraceCallbackData))
+			{
+			case TRACE_Stop:	return false;
+			case TRACE_Abort:	Results->HitType = TRACE_HitNone; return false;
+			case TRACE_Skip:	Results->HitType = TRACE_HitNone; break;
+			default:			break;
+			}
 		}
 		else
 		{
diff --git a/src/p_trace.h b/src/p_trace.h
index 8ce905da3..403b1f9cf 100644
--- a/src/p_trace.h
+++ b/src/p_trace.h
@@ -85,10 +85,20 @@ enum
 	TRACE_Impact		= 4,	// Trigger SPAC_IMPACT lines
 };
 
+// return values from callback
+enum ETraceStatus
+{
+	TRACE_Stop,			// stop the trace, returning this hit
+	TRACE_Continue,		// continue the trace, returning this hit if there are none further along
+	TRACE_Skip,			// continue the trace; do not return this hit
+	TRACE_Abort,		// stop the trace, returning no hits
+};
+
 bool Trace (fixed_t x, fixed_t y, fixed_t z, sector_t *sector,
 			fixed_t vx, fixed_t vy, fixed_t vz, fixed_t maxDist,
 			DWORD ActorMask, DWORD WallMask, AActor *ignore,
 			FTraceResults &res,
-			DWORD traceFlags=0, bool (*callback)(FTraceResults &res)=NULL);
+			DWORD traceFlags=0,
+			ETraceStatus (*callback)(FTraceResults &res, void *)=NULL, void *callbackdata=NULL);
 
 #endif //__P_TRACE_H__