diff --git a/src/p_map.cpp b/src/p_map.cpp
index 16a5933d5a..290b84b9ed 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -860,6 +860,26 @@ bool PIT_CheckLine(FMultiBlockLinesIterator &mit, FMultiBlockLinesIterator::Chec
 	FLineOpening open;
 
 	P_LineOpening(open, tm.thing, ld, ref, &cres.Position, cres.portalflags);
+	if (!tm.thing->Sector->PortalBlocksMovement(sector_t::ceiling))
+	{
+		sector_t *oppsec = cres.line->frontsector == tm.thing->Sector ? cres.line->backsector : cres.line->frontsector;
+		if (oppsec->PortalBlocksMovement(sector_t::ceiling))
+		{
+			double portz = tm.thing->Sector->GetPortalPlaneZ(sector_t::ceiling);
+			if (tm.thing->Z() < portz && tm.thing->Z() + tm.thing->MaxStepHeight >= portz && tm.floorz < portz)
+			{
+				// Actor is stepping through a portal.
+				/*
+				tm.floorz = portz;
+				tm.floorsector = oppsec;
+				tm.floorpic = cres.line->sidedef[0]->GetTexture(side_t::mid);
+				tm.floorterrain = 0;
+				*/
+				tm.portalstep = true;
+				return true;
+			}
+		}
+	}
 
 	// [RH] Steep sectors count as dropoffs, if the actor touches the boundary between a steep slope and something else
 	if (!(tm.thing->flags & MF_DROPOFF) &&
diff --git a/src/portal.cpp b/src/portal.cpp
index f1454cdc6c..156643cfba 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -1231,8 +1231,8 @@ bool P_CollectConnectedGroups(int startgroup, const DVector3 &position, double u
 		{
 			int othergroup = wsec->GetOppositePortalGroup(sector_t::floor);
 			DVector2 pos = Displacements.getOffset(startgroup, othergroup) + position;
-			processMask.setBit(othergroup | FPortalGroupArray::LOWER);
-			out.Add(othergroup);
+			processMask.setBit(othergroup);
+			out.Add(othergroup | FPortalGroupArray::LOWER);
 			wsec = P_PointInSector(pos);	// get lower sector at the exact spot we want to check and repeat
 			retval = true;
 		}