diff --git a/src/p_map.cpp b/src/p_map.cpp
index bce8c77395..eb537a3b18 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -857,6 +857,8 @@ bool PIT_CheckLine(line_t *ld, const FBoundingBox &box, FCheckPosition &tm)
 	fixedvec2 ref = FindRefPoint(ld, rpos);
 	FLineOpening open;
 
+	P_LineOpening(open, tm.thing, ld, ref.x, ref.y, tm.x, tm.y, 0);
+
 	// the floorplane on both sides is identical with the current one
 	// so don't mess around with the z-position.
 	if (ld->frontsector->floorplane == ld->backsector->floorplane &&
diff --git a/src/portal.cpp b/src/portal.cpp
index efd46d8518..62c44ce2f0 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -918,6 +918,8 @@ void P_CreateLinkedPortals()
 	}
 	if (orgs.Size() == 0)
 	{
+		// Create the 0->0 translation which is always needed.
+		Displacements.Create(1);
 		return;
 	}
 	for (int i = 0; i < numsectors; i++)
diff --git a/src/portal.h b/src/portal.h
index c974d8049f..33fb866921 100644
--- a/src/portal.h
+++ b/src/portal.h
@@ -41,6 +41,11 @@ struct FDisplacementTable
 	TArray<FDisplacement> data;
 	int size;
 
+	FDisplacementTable()
+	{
+		Create(1);
+	}
+
 	void Create(int numgroups)
 	{
 		data.Resize(numgroups*numgroups);
@@ -50,6 +55,7 @@ struct FDisplacementTable
 
 	FDisplacement &operator()(int x, int y)
 	{
+		if (x == y) return data[0];	// shortcut for the most common case
 		return data[x + size*y];
 	}
 };