diff --git a/src/actor.h b/src/actor.h
index e7fe048ef9..d369e5fa92 100644
--- a/src/actor.h
+++ b/src/actor.h
@@ -959,11 +959,14 @@ public:
 
 	// Triggers SECSPAC_Exit/SECSPAC_Enter and related events if oldsec != current sector
 	void CheckSectorTransition(sector_t *oldsec);
+	void UpdateRenderSectorList();
+	void ClearRenderSectorList();
 
 // info for drawing
 // NOTE: The first member variable *must* be snext.
 	AActor			*snext, **sprev;	// links in sector (if needed)
 	DVector3		__Pos;		// double underscores so that it won't get used by accident. Access to this should be exclusively through the designated access functions.
+	DVector3		OldRenderPos;
 
 	DRotator		Angles;
 	DVector3		Vel;
@@ -1094,6 +1097,8 @@ public:
 
 	// a linked list of sectors where this object appears
 	struct msecnode_t	*touching_sectorlist;				// phares 3/14/98
+	struct msecnode_t	*render_sectorlist;		// same for cross-portal rendering
+
 
 	TObjPtr<AInventory>	Inventory;		// [RH] This actor's inventory
 	DWORD			InventoryID;	// A unique ID to keep track of inventory items
diff --git a/src/p_local.h b/src/p_local.h
index a5336a9ee1..1a89154956 100644
--- a/src/p_local.h
+++ b/src/p_local.h
@@ -350,7 +350,8 @@ void	P_RadiusAttack (AActor *spot, AActor *source, int damage, int distance,
 
 void	P_DelSector_List();
 void	P_DelSeclist(msecnode_t *);							// phares 3/16/98
-msecnode_t*	P_DelSecnode(msecnode_t *);
+msecnode_t *P_AddSecnode(sector_t *s, AActor *thing, msecnode_t *nextnode, msecnode_t *&sec_thinglist);
+msecnode_t*	P_DelSecnode(msecnode_t *, msecnode_t *sector_t::*head);
 void	P_CreateSecNodeList(AActor*);		// phares 3/14/98
 double	P_GetMoveFactor(const AActor *mo, double *frictionp);	// phares  3/6/98
 double		P_GetFriction(const AActor *mo, double *frictionfactor);
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 8254ac5bb0..d1cd918160 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -5555,6 +5555,7 @@ int P_PushUp(AActor *thing, FChangePosition *cpos)
 			intersect->SetZ(oldz);
 			return 2;
 		}
+		intersect->UpdateRenderSectorList();
 	}
 	thing->CheckPortalTransition(true);
 	return 0;
@@ -5602,6 +5603,7 @@ int P_PushDown(AActor *thing, FChangePosition *cpos)
 				intersect->SetZ(oldz);
 				return 2;
 			}
+			intersect->UpdateRenderSectorList();
 		}
 	}
 	thing->CheckPortalTransition(true);
@@ -5634,6 +5636,7 @@ void PIT_FloorDrop(AActor *thing, FChangePosition *cpos)
 		{
 			thing->SetZ(thing->floorz);
 			P_CheckFakeFloorTriggers(thing, oldz);
+			thing->UpdateRenderSectorList();
 		}
 	}
 	else if ((thing->Z() != oldfloorz && !(thing->flags & MF_NOLIFTDROP)))
@@ -5642,6 +5645,7 @@ void PIT_FloorDrop(AActor *thing, FChangePosition *cpos)
 		{
 			thing->AddZ(-oldfloorz + thing->floorz);
 			P_CheckFakeFloorTriggers(thing, oldz);
+			thing->UpdateRenderSectorList();
 		}
 	}
 	if (thing->player && thing->player->mo == thing)
@@ -5689,10 +5693,12 @@ void PIT_FloorRaise(AActor *thing, FChangePosition *cpos)
 	{
 	default:
 		P_CheckFakeFloorTriggers(thing, oldz);
+		thing->UpdateRenderSectorList();
 		break;
 	case 1:
 		P_DoCrunch(thing, cpos);
 		P_CheckFakeFloorTriggers(thing, oldz);
+		thing->UpdateRenderSectorList();
 		break;
 	case 2:
 		P_DoCrunch(thing, cpos);
@@ -5735,6 +5741,7 @@ void PIT_CeilingLower(AActor *thing, FChangePosition *cpos)
 		{
 			thing->SetZ(thing->floorz);
 		}
+		thing->UpdateRenderSectorList();
 		switch (P_PushDown(thing, cpos))
 		{
 		case 2:
@@ -5744,9 +5751,11 @@ void PIT_CeilingLower(AActor *thing, FChangePosition *cpos)
 				thing->SetZ(thing->floorz);
 			P_DoCrunch(thing, cpos);
 			P_CheckFakeFloorTriggers(thing, oldz);
+			thing->UpdateRenderSectorList();
 			break;
 		default:
 			P_CheckFakeFloorTriggers(thing, oldz);
+			thing->UpdateRenderSectorList();
 			break;
 		}
 	}
@@ -5782,6 +5791,7 @@ void PIT_CeilingRaise(AActor *thing, FChangePosition *cpos)
 			thing->SetZ(thing->ceilingz - thing->Height);
 		}
 		P_CheckFakeFloorTriggers(thing, oldz);
+		thing->UpdateRenderSectorList();
 	}
 	else if ((thing->flags2 & MF2_PASSMOBJ) && !isgood && thing->Top() < thing->ceilingz)
 	{
@@ -5789,6 +5799,7 @@ void PIT_CeilingRaise(AActor *thing, FChangePosition *cpos)
 		if (!P_TestMobjZ(thing, true, &onmobj) && onmobj->Z() <= thing->Z())
 		{
 			thing->SetZ(MIN(thing->ceilingz - thing->Height, onmobj->Top()));
+			thing->UpdateRenderSectorList();
 		}
 	}
 	if (thing->player && thing->player->mo == thing)
@@ -6023,7 +6034,7 @@ void P_PutSecnode(msecnode_t *node)
 //
 //=============================================================================
 
-msecnode_t *P_AddSecnode(sector_t *s, AActor *thing, msecnode_t *nextnode)
+msecnode_t *P_AddSecnode(sector_t *s, AActor *thing, msecnode_t *nextnode, msecnode_t *&sec_thinglist)
 {
 	msecnode_t *node;
 
@@ -6061,10 +6072,10 @@ msecnode_t *P_AddSecnode(sector_t *s, AActor *thing, msecnode_t *nextnode)
 	// Add new node at head of sector thread starting at s->touching_thinglist
 
 	node->m_sprev = NULL;			// prev node on sector thread
-	node->m_snext = s->touching_thinglist; // next node on sector thread
-	if (s->touching_thinglist)
+	node->m_snext = sec_thinglist; // next node on sector thread
+	if (sec_thinglist)
 		node->m_snext->m_sprev = node;
-	s->touching_thinglist = node;
+	sec_thinglist = node;
 	return node;
 }
 
@@ -6078,7 +6089,7 @@ msecnode_t *P_AddSecnode(sector_t *s, AActor *thing, msecnode_t *nextnode)
 //
 //=============================================================================
 
-msecnode_t *P_DelSecnode(msecnode_t *node)
+msecnode_t *P_DelSecnode(msecnode_t *node, msecnode_t *sector_t::*listhead)
 {
 	msecnode_t* tp;  // prev node on thing thread
 	msecnode_t* tn;  // next node on thing thread
@@ -6105,7 +6116,7 @@ msecnode_t *P_DelSecnode(msecnode_t *node)
 		if (sp)
 			sp->m_snext = sn;
 		else
-			node->m_sector->touching_thinglist = sn;
+			node->m_sector->*listhead = sn;
 		if (sn)
 			sn->m_sprev = sp;
 
@@ -6145,7 +6156,7 @@ void P_DelSector_List()
 void P_DelSeclist(msecnode_t *node)
 {
 	while (node)
-		node = P_DelSecnode(node);
+		node = P_DelSecnode(node, &sector_t::touching_thinglist);
 }
 
 //=============================================================================
@@ -6173,13 +6184,15 @@ void P_CreateSecNodeList(AActor *thing)
 		node = node->m_tnext;
 	}
 
-	FBoundingBox box(thing->X(), thing->Y(), thing->radius);
-	FBlockLinesIterator it(box);
-	line_t *ld;
+	FPortalGroupArray grouplist;
+	FMultiBlockLinesIterator mit(grouplist, thing);
+	FMultiBlockLinesIterator::CheckResult cres;
 
-	while ((ld = it.Next()))
+	while (mit.Next(&cres))
 	{
-		if (!box.inRange(ld) || box.BoxOnLineSide(ld) != -1)
+		line_t *ld = cres.line;
+
+		if (!mit.Box().inRange(ld) || mit.Box().BoxOnLineSide(ld) != -1)
 			continue;
 
 		// This line crosses through the object.
@@ -6189,7 +6202,7 @@ void P_CreateSecNodeList(AActor *thing)
 		// allowed to move to this position, then the sector_list
 		// will be attached to the Thing's AActor at touching_sectorlist.
 
-		sector_list = P_AddSecnode(ld->frontsector, thing, sector_list);
+		sector_list = P_AddSecnode(ld->frontsector, thing, sector_list, ld->frontsector->touching_thinglist);
 
 		// Don't assume all lines are 2-sided, since some Things
 		// like MT_TFOG are allowed regardless of whether their radius takes
@@ -6199,12 +6212,12 @@ void P_CreateSecNodeList(AActor *thing)
 		// Use sidedefs instead of 2s flag to determine two-sidedness.
 
 		if (ld->backsector)
-			sector_list = P_AddSecnode(ld->backsector, thing, sector_list);
+			sector_list = P_AddSecnode(ld->backsector, thing, sector_list, ld->backsector->touching_thinglist);
 	}
 
 	// Add the sector of the (x,y) point to sector_list.
 
-	sector_list = P_AddSecnode(thing->Sector, thing, sector_list);
+	sector_list = P_AddSecnode(thing->Sector, thing, sector_list, thing->Sector->touching_thinglist);
 
 	// Now delete any nodes that won't be used. These are the ones where
 	// m_thing is still NULL.
@@ -6216,7 +6229,7 @@ void P_CreateSecNodeList(AActor *thing)
 		{
 			if (node == sector_list)
 				sector_list = node->m_tnext;
-			node = P_DelSecnode(node);
+			node = P_DelSecnode(node, &sector_t::touching_thinglist);
 		}
 		else
 		{
@@ -6225,6 +6238,54 @@ void P_CreateSecNodeList(AActor *thing)
 	}
 }
 
+
+//==========================================================================
+//
+// Handle the lists used to render actors from other portal areas
+//
+//==========================================================================
+
+void AActor::UpdateRenderSectorList()
+{
+	static const double SPRITE_SPACE = 64.;
+	if (Pos() != OldRenderPos)
+	{
+		sector_t *sec = Sector;
+		double lasth = -FLT_MAX;
+		ClearRenderSectorList();
+		while (!sec->PortalBlocksMovement(sector_t::ceiling))
+		{
+			double planeh = sec->SkyBoxes[sector_t::ceiling]->specialf1;
+			if (planeh < lasth) break;	// broken setup.
+			if (Top() + SPRITE_SPACE < planeh) break;
+			lasth = planeh;
+			DVector2 newpos = Pos() + sec->SkyBoxes[sector_t::ceiling]->Scale;
+			sec = P_PointInSector(newpos);
+			render_sectorlist = P_AddSecnode(sec, this, render_sectorlist, sec->render_thinglist);
+		}
+		lasth = FLT_MAX;
+		while (!sec->PortalBlocksMovement(sector_t::floor))
+		{
+			double planeh = sec->SkyBoxes[sector_t::floor]->specialf1;
+			if (planeh > lasth) break;	// broken setup.
+			if (Z() - SPRITE_SPACE > planeh) break;
+			lasth = planeh;
+			DVector2 newpos = Pos() + sec->SkyBoxes[sector_t::floor]->Scale;
+			sec = P_PointInSector(newpos);
+			render_sectorlist = P_AddSecnode(sec, this, render_sectorlist, sec->render_thinglist);
+		}
+	}
+}
+
+void AActor::ClearRenderSectorList()
+{
+	msecnode_t *node = render_sectorlist;
+	while (node)
+		node = P_DelSecnode(node, &sector_t::render_thinglist);
+	render_sectorlist = NULL;
+}
+
+
 //==========================================================================
 //
 //
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index f018be55b5..18caa2f3c1 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -3752,6 +3752,9 @@ void AActor::Tick ()
 	if (!CheckNoDelay())
 		return; // freed itself
 	// cycle through states, calling action functions at transitions
+
+	UpdateRenderSectorList();
+
 	if (tics != -1)
 	{
 		// [RH] Use tics <= 0 instead of == 0 so that spawnstates
@@ -4011,6 +4014,7 @@ AActor *AActor::StaticSpawn (PClassActor *type, const DVector3 &pos, replace_t a
 	}
 
 	actor->SetXYZ(pos);
+	actor->OldRenderPos = { FLT_MAX, FLT_MAX, FLT_MAX };
 	actor->picnum.SetInvalid();
 	actor->health = actor->SpawnHealth();
 
@@ -4322,12 +4326,15 @@ void AActor::Deactivate (AActor *activator)
 	}
 }
 
+
 //
 // P_RemoveMobj
 //
 
 void AActor::Destroy ()
 {
+	ClearRenderSectorList();
+
 	// [RH] Destroy any inventory this actor is carrying
 	DestroyAllInventory ();
 
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 148dcbea85..718e54e9b6 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -1510,6 +1510,7 @@ void P_LoadSectors (MapData *map, FMissingTextureTracker &missingtex)
 		tagManager.AddSectorTag(i, LittleShort(ms->tag));
 		ss->thinglist = NULL;
 		ss->touching_thinglist = NULL;		// phares 3/14/98
+		ss->render_thinglist = NULL;
 		ss->seqType = defSeqType;
 		ss->SeqName = NAME_None;
 		ss->nextsec = -1;	//jff 2/26/98 add fields to support locking out
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 017f73cf15..20852a5858 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1291,6 +1291,7 @@ public:
 		sec->SetAlpha(sector_t::ceiling, 1.);
 		sec->thinglist = NULL;
 		sec->touching_thinglist = NULL;		// phares 3/14/98
+		sec->render_thinglist = NULL;
 		sec->seqType = (level.flags & LEVEL_SNDSEQTOTALCTRL) ? 0 : -1;
 		sec->nextsec = -1;	//jff 2/26/98 add fields to support locking out
 		sec->prevsec = -1;	// stair retriggering until build completes
diff --git a/src/p_user.cpp b/src/p_user.cpp
index 30a849b846..4860440704 100644
--- a/src/p_user.cpp
+++ b/src/p_user.cpp
@@ -2860,8 +2860,6 @@ void P_PredictPlayer (player_t *player)
 	}
 }
 
-extern msecnode_t *P_AddSecnode (sector_t *s, AActor *thing, msecnode_t *nextnode);
-
 void P_UnPredictPlayer ()
 {
 	player_t *player = &players[consoleplayer];
@@ -2922,7 +2920,7 @@ void P_UnPredictPlayer ()
 			sector_list = NULL;
 			for (i = PredictionTouchingSectorsBackup.Size(); i-- > 0;)
 			{
-				sector_list = P_AddSecnode(PredictionTouchingSectorsBackup[i], act, sector_list);
+				sector_list = P_AddSecnode(PredictionTouchingSectorsBackup[i], act, sector_list, PredictionTouchingSectorsBackup[i]->touching_thinglist);
 			}
 			act->touching_sectorlist = sector_list;	// Attach to thing
 			sector_list = NULL;		// clear for next time
@@ -2934,7 +2932,7 @@ void P_UnPredictPlayer ()
 				{
 					if (node == sector_list)
 						sector_list = node->m_tnext;
-					node = P_DelSecnode(node);
+					node = P_DelSecnode(node, &sector_t::touching_thinglist);
 				}
 				else
 				{
diff --git a/src/r_defs.h b/src/r_defs.h
index 2b7b4a218f..79af0929f2 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -1057,6 +1057,7 @@ public:
 	// list of mobjs that are at least partially in the sector
 	// thinglist is a subset of touching_thinglist
 	struct msecnode_t *touching_thinglist;				// phares 3/14/98
+	struct msecnode_t *render_thinglist;				// for cross-portal rendering.
 
 	double gravity;			// [RH] Sector gravity (1.0 is normal)
 	FNameNoInit damagetype;		// [RH] Means-of-death for applied damage