diff --git a/source/core/maploader.cpp b/source/core/maploader.cpp
index 602775168..6b7ff51e0 100644
--- a/source/core/maploader.cpp
+++ b/source/core/maploader.cpp
@@ -763,14 +763,27 @@ void setWallSectors()
 		i++;
 	}
 
-	for (unsigned i = 1; i < wall.Size() - 1; i++)
+	// 
+	for (unsigned ii = 1; ii < wall.Size() - 1; ii++)
 	{
 		// two maps in RRRA have this error. Delete one of those 2 walls.
-		if (wall[i].point2 == wall[i + 1].point2)
+		if (wall[ii].point2 == wall[ii + 1].point2)
 		{
-			wall[i].nextwall = -1;
-			wall[i].nextsector = -1;
-			wall[i].point2 = i;
+			auto w1 = wall[ii].lastWall(false);
+			auto w2 = wall[ii + 1].lastWall(false);
+			// Neutralize the bad one of the two walls.
+			if (w1 == nullptr)
+			{
+				wall[ii].nextwall = -1;
+				wall[ii].nextsector = -1;
+				wall[ii].point2 = ii;
+			}
+			else if (w2 == nullptr)
+			{
+				wall[ii+1].nextwall = -1;
+				wall[ii+1].nextsector = -1;
+				wall[ii+1].point2 = ii;
+			}
 		}
 	}
 
diff --git a/source/core/maptypes.h b/source/core/maptypes.h
index 5a7b915c8..c695b069b 100644
--- a/source/core/maptypes.h
+++ b/source/core/maptypes.h
@@ -391,7 +391,7 @@ struct walltype
 	sectortype* nextSector() const;
 	sectortype* sectorp() const;
 	walltype* nextWall() const;
-	walltype* lastWall() const;
+	walltype* lastWall(bool fast  = true) const;
 	walltype* point2Wall() const;
 	vec2_t delta() const { return point2Wall()->pos - pos; }
 	vec2_t center() const { return(point2Wall()->pos + pos) / 2; }
@@ -671,10 +671,10 @@ inline sectortype* walltype::sectorp() const
 	return &::sector[sector]; // cannot be -1 in a proper map.
 }
 
-inline walltype* walltype::lastWall() const
+inline walltype* walltype::lastWall(bool fast) const
 {
 	int index = wall.IndexOf(this);
-	if (index > 0 && wall[index - 1].point2 == index) return &wall[index - 1];
+	if (fast && index > 0 && wall[index - 1].point2 == index) return &wall[index - 1];
 
 	int check = index;
 	for (int i = 0; i < 16384; i++)	// don't run endlessly in case of malformed sectors.