diff --git a/src/b_func.cpp b/src/b_func.cpp
index adaa755c2..efc3f7f57 100644
--- a/src/b_func.cpp
+++ b/src/b_func.cpp
@@ -118,7 +118,7 @@ bool FCajunMaster::Reachable (AActor *looker, AActor *rtarget)
 //in doom is 90 degrees infront.
 bool FCajunMaster::Check_LOS (AActor *from, AActor *to, angle_t vangle)
 {
-	if (!P_CheckSight (from, to, 2))
+	if (!P_CheckSight (from, to, SF_SEEPASTBLOCKEVERYTHING))
 		return false; // out of sight
 	if (vangle == ANGLE_MAX)
 		return true;
@@ -339,7 +339,7 @@ AActor *FCajunMaster::Choose_Mate (AActor *bot)
 			&& !p_leader[count]) //taken?
 		{
 
-			if (P_CheckSight (bot, client->mo, 1))
+			if (P_CheckSight (bot, client->mo, SF_IGNOREVISIBILITY))
 			{
 				test = P_AproxDistance (client->mo->x - bot->x,
 										client->mo->y - bot->y);
@@ -525,7 +525,7 @@ angle_t FCajunMaster::FireRox (AActor *bot, AActor *enemy, ticcmd_t *cmd)
 			   enemy->y + FixedMul(enemy->vely, (m+2*FRACUNIT)), ONFLOORZ, 1);
 	dist = P_AproxDistance(actor->x-bglobal.body1->x, actor->y-bglobal.body1->y);
 	//try the predicted location
-	if (P_CheckSight (actor, bglobal.body1, 1)) //See the predicted location, so give a test missile
+	if (P_CheckSight (actor, bglobal.body1, SF_IGNOREVISIBILITY)) //See the predicted location, so give a test missile
 	{
 		FCheckPosition tm;
 		if (SafeCheckPosition (bot, actor->x, actor->y, tm))
diff --git a/src/p_enemy.cpp b/src/p_enemy.cpp
index eff234af9..422ed845c 100644
--- a/src/p_enemy.cpp
+++ b/src/p_enemy.cpp
@@ -198,16 +198,16 @@ void P_RecursiveSound (sector_t *sec, AActor *soundtarget, bool splash, int soun
 //
 //----------------------------------------------------------------------------
 
-void P_NoiseAlert (AActor *target, AActor *emmiter, bool splash)
+void P_NoiseAlert (AActor *target, AActor *emitter, bool splash)
 {
-	if (emmiter == NULL)
+	if (emitter == NULL)
 		return;
 
 	if (target != NULL && target->player && (target->player->cheats & CF_NOTARGET))
 		return;
 
 	validcount++;
-	P_RecursiveSound (emmiter->Sector, target, splash, 0);
+	P_RecursiveSound (emitter->Sector, target, splash, 0);
 }
 
 
@@ -308,7 +308,7 @@ bool P_CheckMissileRange (AActor *actor)
 {
 	fixed_t dist;
 		
-	if (!P_CheckSight (actor, actor->target, 4))
+	if (!P_CheckSight (actor, actor->target, SF_SEEPASTBLOCKEVERYTHING|SF_SEEPASTSHOOTABLELINES))
 		return false;
 		
 	if (actor->flags & MF_JUSTHIT)
@@ -1136,7 +1136,7 @@ bool P_IsVisible(AActor *lookee, AActor *other, INTBOOL allaround, FLookExParams
 	}
 
 	// P_CheckSight is by far the most expensive operation in here so let's do it last.
-	return P_CheckSight(lookee, other, 2);
+	return P_CheckSight(lookee, other, SF_SEEPASTBLOCKEVERYTHING);
 }
 
 //---------------------------------------------------------------------------
@@ -1154,7 +1154,7 @@ bool P_LookForMonsters (AActor *actor)
 	AActor *mo;
 	TThinkerIterator<AActor> iterator;
 
-	if (!P_CheckSight (players[0].mo, actor, 2))
+	if (!P_CheckSight (players[0].mo, actor, SF_SEEPASTBLOCKEVERYTHING))
 	{ // Player can't see monster
 		return false;
 	}
@@ -1183,7 +1183,7 @@ bool P_LookForMonsters (AActor *actor)
 		{ // [RH] Don't go after same species
 			continue;
 		}
-		if (!P_CheckSight (actor, mo, 2))
+		if (!P_CheckSight (actor, mo, SF_SEEPASTBLOCKEVERYTHING))
 		{ // Out of sight
 			continue;
 		}
@@ -1764,7 +1764,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_Look)
 
 			if (self->flags & MF_AMBUSH)
 			{
-				if (P_CheckSight (self, self->target, 2))
+				if (P_CheckSight (self, self->target, SF_SEEPASTBLOCKEVERYTHING))
 					goto seeyou;
 			}
 			else
@@ -1931,7 +1931,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_LookEx)
 				{
 					dist = P_AproxDistance (self->target->x - self->x,
 											self->target->y - self->y);
-					if (P_CheckSight (self, self->target, 2) &&
+					if (P_CheckSight (self, self->target, SF_SEEPASTBLOCKEVERYTHING) &&
 						(!minseedist || dist > minseedist) &&
 						(!maxseedist || dist < maxseedist))
 					{
@@ -2062,7 +2062,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_Look2)
 		{
 			if (self->flags & MF_AMBUSH)
 			{
-				if (!P_CheckSight (self, targ, 2))
+				if (!P_CheckSight (self, targ, SF_SEEPASTBLOCKEVERYTHING))
 					goto nosee;
 			}
 			self->target = targ;
diff --git a/src/p_local.h b/src/p_local.h
index 1707db26e..134a627ed 100644
--- a/src/p_local.h
+++ b/src/p_local.h
@@ -390,6 +390,15 @@ void	P_SlideMove (AActor* mo, fixed_t tryx, fixed_t tryy, int numsteps);
 bool	P_BounceWall (AActor *mo);
 bool	P_BounceActor (AActor *mo, AActor * BlockingMobj);
 bool	P_CheckSight (const AActor* t1, const AActor* t2, int flags=0);
+
+enum ESightFlags
+{
+	SF_IGNOREVISIBILITY=1,
+	SF_SEEPASTSHOOTABLELINES=2,
+	SF_SEEPASTBLOCKEVERYTHING=4,
+	SF_IGNOREWATERBOUNDARY=8
+};
+
 void	P_ResetSightCounters (bool full);
 bool	P_TalkFacing (AActor *player);
 void	P_UseLines (player_t* player);
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 019c8087a..5759f59c0 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -3053,7 +3053,7 @@ void aim_t::AimTraverse (fixed_t startx, fixed_t starty, fixed_t endx, fixed_t e
 		if (crossedffloors)
 		{
 			// if 3D floors were in the way do an extra visibility check for safety
-			if (!P_CheckSight(shootthing, th, 1)) 
+			if (!P_CheckSight(shootthing, th, SF_IGNOREVISIBILITY|SF_IGNOREWATERBOUNDARY)) 
 			{
 				// the thing can't be seen so we can safely exclude its range from our aiming field
 				if (thingtoppitch<toppitch) 
@@ -4324,7 +4324,7 @@ void P_RadiusAttack (AActor *bombspot, AActor *bombsource, int bombdamage, int b
 			}
 			points *= thing->GetClass()->Meta.GetMetaFixed(AMETA_RDFactor, FRACUNIT)/(float)FRACUNIT;
 
-			if (points > 0.f && P_CheckSight (thing, bombspot, 1))
+			if (points > 0.f && P_CheckSight (thing, bombspot, SF_IGNOREVISIBILITY|SF_IGNOREWATERBOUNDARY))
 			{ // OK to damage; target is in direct path
 				float velz;
 				float thrust;
@@ -4382,7 +4382,7 @@ void P_RadiusAttack (AActor *bombspot, AActor *bombsource, int bombdamage, int b
 			if (dist >= bombdistance)
 				continue;  // out of range
 
-			if (P_CheckSight (thing, bombspot, 1))
+			if (P_CheckSight (thing, bombspot, SF_IGNOREVISIBILITY|SF_IGNOREWATERBOUNDARY))
 			{ // OK to damage; target is in direct path
 				dist = clamp<int>(dist - fulldamagedistance, 0, dist);
 				int damage = Scale (bombdamage, bombdistance-dist, bombdistance);
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index ae376f148..a3d739bea 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -3016,7 +3016,7 @@ void AActor::Tick ()
 						&& !players[i].enemy
 						&& player ? !IsTeammate (players[i].mo) : true
 						&& P_AproxDistance (players[i].mo->x-x, players[i].mo->y-y) < MAX_MONSTER_TARGET_DIST
-						&& P_CheckSight (players[i].mo, this, 2))
+						&& P_CheckSight (players[i].mo, this, SF_SEEPASTBLOCKEVERYTHING))
 					{ //Probably a monster, so go kill it.
 						players[i].enemy = this;
 					}
diff --git a/src/p_sight.cpp b/src/p_sight.cpp
index cc2940d7d..55ab3f13a 100644
--- a/src/p_sight.cpp
+++ b/src/p_sight.cpp
@@ -53,7 +53,7 @@ class SightCheck
 	fixed_t lastzbottom;				// z at last line
 	sector_t * lastsector;			// last sector being entered by trace
 	fixed_t topslope, bottomslope;	// slopes to top and bottom of target
-	int SeePastBlockEverything, SeePastShootableLines;
+	int Flags;
 	divline_t trace;
 	int myseethrough;
 
@@ -73,9 +73,8 @@ public:
 		seeingthing=t2;
 		bottomslope = t2->z - sightzstart;
 		topslope = bottomslope + t2->height;
+		Flags = flags;
 
-		SeePastBlockEverything = flags & 6;
-		SeePastShootableLines = flags & 4;
 		myseethrough = FF_SEETHROUGH;
 	}
 };
@@ -144,6 +143,7 @@ bool SightCheck::PTR_SightTraverse (intercept_t *in)
 				F3DFloor*  rover=s->e->XFloor.ffloors[j];
 
 				if((rover->flags & FF_SEETHROUGH) == myseethrough || !(rover->flags & FF_EXISTS)) continue;
+				if ((Flags & SF_IGNOREWATERBOUNDARY) && (rover->flags & FF_SOLID) == 0) continue;
 				
 				fixed_t ff_bottom=rover->bottom.plane->ZatPoint(trX, trY);
 				fixed_t ff_top=rover->top.plane->ZatPoint(trX, trY);
@@ -176,6 +176,7 @@ bool SightCheck::PTR_SightTraverse (intercept_t *in)
 						F3DFloor*  rover2=sb->e->XFloor.ffloors[k];
 
 						if((rover2->flags & FF_SEETHROUGH) == myseethrough || !(rover2->flags & FF_EXISTS)) continue;
+						if ((Flags & SF_IGNOREWATERBOUNDARY) && (rover->flags & FF_SOLID) == 0) continue;
 						
 						fixed_t ffb_bottom=rover2->bottom.plane->ZatPoint(trX, trY);
 						fixed_t ffb_top=rover2->top.plane->ZatPoint(trX, trY);
@@ -255,7 +256,7 @@ bool SightCheck::P_SightCheckLine (line_t *ld)
 	// [RH] don't see past block everything lines
 	if (ld->flags & ML_BLOCKEVERYTHING)
 	{
-		if (!SeePastBlockEverything)
+		if (!(Flags & SF_SEEPASTBLOCKEVERYTHING))
 		{
 			return false;
 		}
@@ -263,7 +264,7 @@ bool SightCheck::P_SightCheckLine (line_t *ld)
 		// that runs a script on the current map. Used to prevent monsters
 		// from trying to attack through a block everything line unless
 		// there's a chance their attack will make it nonblocking.
-		if (!SeePastShootableLines)
+		if (!(Flags & SF_SEEPASTSHOOTABLELINES))
 		{
 			if (!(ld->activation & SPAC_Impact))
 			{
@@ -407,6 +408,7 @@ bool SightCheck::P_SightTraverseIntercepts ()
 			F3DFloor*  rover = lastsector->e->XFloor.ffloors[i];
 
 			if((rover->flags & FF_SOLID) == myseethrough || !(rover->flags & FF_EXISTS)) continue;
+			if ((Flags & SF_IGNOREWATERBOUNDARY) && (rover->flags & FF_SOLID) == 0) continue;
 			
 			fixed_t ff_bottom=rover->bottom.plane->ZatPoint(seeingthing->x, seeingthing->y);
 			fixed_t ff_top=rover->top.plane->ZatPoint(seeingthing->x, seeingthing->y);
@@ -670,7 +672,7 @@ sightcounts[0]++;
 //
 	// [RH] Andy Baker's stealth monsters:
 	// Cannot see an invisible object
-	if ((flags & 1) == 0 && ((t2->renderflags & RF_INVISIBLE) || !t2->RenderStyle.IsVisible(t2->alpha)))
+	if ((flags & SF_IGNOREVISIBILITY) == 0 && ((t2->renderflags & RF_INVISIBLE) || !t2->RenderStyle.IsVisible(t2->alpha)))
 	{ // small chance of an attack being made anyway
 		if ((bglobal.m_Thinking ? pr_botchecksight() : pr_checksight()) > 50)
 		{
@@ -681,20 +683,23 @@ sightcounts[0]++;
 
 	// killough 4/19/98: make fake floors and ceilings block monster view
 
-	if ((s1->GetHeightSec() &&
-		((t1->z + t1->height <= s1->heightsec->floorplane.ZatPoint (t1->x, t1->y) &&
-		  t2->z >= s1->heightsec->floorplane.ZatPoint (t2->x, t2->y)) ||
-		 (t1->z >= s1->heightsec->ceilingplane.ZatPoint (t1->x, t1->y) &&
-		  t2->z + t1->height <= s1->heightsec->ceilingplane.ZatPoint (t2->x, t2->y))))
-		||
-		(s2->GetHeightSec() &&
-		 ((t2->z + t2->height <= s2->heightsec->floorplane.ZatPoint (t2->x, t2->y) &&
-		   t1->z >= s2->heightsec->floorplane.ZatPoint (t1->x, t1->y)) ||
-		  (t2->z >= s2->heightsec->ceilingplane.ZatPoint (t2->x, t2->y) &&
-		   t1->z + t2->height <= s2->heightsec->ceilingplane.ZatPoint (t1->x, t1->y)))))
+	if (!(flags & SF_IGNOREWATERBOUNDARY))
 	{
-		res = false;
-		goto done;
+		if ((s1->GetHeightSec() &&
+			((t1->z + t1->height <= s1->heightsec->floorplane.ZatPoint (t1->x, t1->y) &&
+			  t2->z >= s1->heightsec->floorplane.ZatPoint (t2->x, t2->y)) ||
+			 (t1->z >= s1->heightsec->ceilingplane.ZatPoint (t1->x, t1->y) &&
+			  t2->z + t1->height <= s1->heightsec->ceilingplane.ZatPoint (t2->x, t2->y))))
+			||
+			(s2->GetHeightSec() &&
+			 ((t2->z + t2->height <= s2->heightsec->floorplane.ZatPoint (t2->x, t2->y) &&
+			   t1->z >= s2->heightsec->floorplane.ZatPoint (t1->x, t1->y)) ||
+			  (t2->z >= s2->heightsec->ceilingplane.ZatPoint (t2->x, t2->y) &&
+			   t1->z + t2->height <= s2->heightsec->ceilingplane.ZatPoint (t1->x, t1->y)))))
+		{
+			res = false;
+			goto done;
+		}
 	}
 
 	// An unobstructed LOS is possible.
diff --git a/src/p_spec.cpp b/src/p_spec.cpp
index 95bee9eb3..737ccc226 100644
--- a/src/p_spec.cpp
+++ b/src/p_spec.cpp
@@ -1939,7 +1939,7 @@ void DPusher::Tick ()
 				// If speed <= 0, you're outside the effective radius. You also have
 				// to be able to see the push/pull source point.
 
-				if ((speed > 0) && (P_CheckSight (thing, m_Source, 1)))
+				if ((speed > 0) && (P_CheckSight (thing, m_Source, SF_IGNOREVISIBILITY)))
 				{
 					angle_t pushangle = R_PointToAngle2 (thing->x, thing->y, sx, sy);
 					if (m_Source->GetClass()->TypeName == NAME_PointPusher)
diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/thingdef/thingdef_codeptr.cpp
index 7e5f92f3c..59ca172cb 100644
--- a/src/thingdef/thingdef_codeptr.cpp
+++ b/src/thingdef/thingdef_codeptr.cpp
@@ -1891,9 +1891,9 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_CheckSight)
 
 	ACTION_SET_RESULT(false);	// Jumps should never set the result for inventory state chains!
 
-	for (int i=0;i<MAXPLAYERS;i++) 
+	for (int i = 0; i < MAXPLAYERS; i++) 
 	{
-		if (playeringame[i] && P_CheckSight(players[i].camera,self,true)) return;
+		if (playeringame[i] && P_CheckSight(players[i].camera, self, SF_IGNOREVISIBILITY)) return;
 	}
 
 	ACTION_JUMP(jump);
@@ -1944,7 +1944,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_CheckSightOrRange)
 			}
 
 			// Now check LOS.
-			if (P_CheckSight(camera, self, true))
+			if (P_CheckSight(camera, self, SF_IGNOREVISIBILITY))
 			{ // Visible
 				return;
 			}
@@ -2395,7 +2395,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_JumpIfTargetInLOS)
 
 		if (!target) return; // [KS] Let's not call P_CheckSight unnecessarily in this case.
 
-		if (!P_CheckSight (self, target, 1))
+		if (!P_CheckSight (self, target, SF_IGNOREVISIBILITY))
 			return;
 
 		if (fov && (fov < ANGLE_MAX))
@@ -2458,7 +2458,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_JumpIfInTargetLOS)
 
 	if (!target) return; // [KS] Let's not call P_CheckSight unnecessarily in this case.
 
-	if (!P_CheckSight (target, self, 1))
+	if (!P_CheckSight (target, self, SF_IGNOREVISIBILITY))
 		return;
 
 	if (fov && (fov < ANGLE_MAX))