diff --git a/main/render.c b/main/render.c
index 8075f7f07..27fc22631 100755
--- a/main/render.c
+++ b/main/render.c
@@ -1325,6 +1325,10 @@ int find_seg_side(segment *seg,short *verts,int notside)
 	}
 }
 
+#ifdef OGL
+extern int wall_maybe_4d;
+#endif
+
 //find the two segments that join a given seg though two sides, and
 //the sides of those segments the abut. 
 int find_joining_side_norms(vms_vector *norm0_0,vms_vector *norm0_1,vms_vector *norm1_0,vms_vector *norm1_1,vms_vector **pnt0,vms_vector **pnt1,segment *seg,int s0,int s1)
@@ -1405,9 +1409,12 @@ int find_joining_side_norms(vms_vector *norm0_0,vms_vector *norm0_1,vms_vector *
 
 #ifdef OGL
 	/* ZICO - experimental HACK
-	   If edge_verts differ +/- 100 it's mostly an indication of overlapping rooms using the 4D effect. So we don't want GL_LEQUAL.  It does also happen on other places in a level. But it's *unlikely* we see a portal bug caused by missing GL_LEQUAL with verts that differ that much. Nevertheless it's a simple hack to prevent unwanted textures in 4D rooms. */
-	if ((edge_verts[0] - edge_verts[1] >= 100) || (edge_verts[0] - edge_verts[1] <= -100))
-		glDepthFunc(GL_ALWAYS);
+	   If edge_verts differ +/- 100 it's mostly an indication of overlapping rooms using the 4D effect. So we don't want GL_LEQUAL. So we set wall_maybe_4d causes GL_ALWAYS in wall.c if WALL_ILLUSION */
+	if (((edge_verts[0] - edge_verts[1] >= 100) || (edge_verts[0] - edge_verts[1] <= -100)))
+	{
+		wall_maybe_4d=1;
+	}
+
 #endif
 
 	return 1;
diff --git a/main/wall.c b/main/wall.c
index e03a0611c..db51ab32d 100755
--- a/main/wall.c
+++ b/main/wall.c
@@ -147,6 +147,9 @@ static char rcsid[] = "$Id: wall.c,v 1.1.1.1 2006/03/17 19:44:01 zicodxx Exp $";
 #include "newdemo.h"
 #include "multi.h"
 #include "gameseq.h"
+#ifdef OGL
+#include "ogl_init.h"
+#endif
 
 void kill_stuck_objects(int wallnum);
 
@@ -171,6 +174,9 @@ int Num_open_doors;						// Number of open doors
 
 //#define BM_FLAG_TRANSPARENT			1
 //#define BM_FLAG_SUPER_TRANSPARENT	2
+#ifdef OGL
+int wall_maybe_4d = 0;
+#endif
 
 #ifdef EDITOR
 char	Wall_names[7][10] = {
@@ -215,6 +221,7 @@ int check_transparency( segment * seg, int side )
 //		WID_ILLUSORY_WALL			3	//	1/1/0		illusory wall
 //		WID_TRANSILLUSORY_WALL	7	//	1/1/1		transparent illusory wall
 //		WID_NO_WALL					5	//	1/0/1		no wall, can fly through
+
 int wall_is_doorway ( segment * seg, int side )
 {
 	int flags, type;
@@ -240,15 +247,23 @@ int wall_is_doorway ( segment * seg, int side )
 		return WID_NO_WALL;
 
 	if (type == WALL_ILLUSION) {
+#ifdef OGL
+		if(wall_maybe_4d)
+			glDepthFunc(GL_ALWAYS);
+#endif
 		if (Walls[seg->sides[side].wall_num].flags & WALL_ILLUSION_OFF)
 			return WID_NO_WALL;
 		else {
-			if (check_transparency( seg, side))
+			if (check_transparency( seg, side)) {
 				return WID_TRANSILLUSORY_WALL;
-		 	else
+		 	}else
 				return WID_ILLUSORY_WALL;
 		}
 	}
+#ifdef OGL
+	else
+		wall_maybe_4d=0;
+#endif
 
 	if (type == WALL_BLASTABLE) {
 	 	if (flags & WALL_BLASTED)