diff --git a/src/p_slopes.c b/src/p_slopes.c
index 9cd22f35..60bd1087 100644
--- a/src/p_slopes.c
+++ b/src/p_slopes.c
@@ -204,6 +204,8 @@ void P_SpawnSlope_Line(int linenum)
 	// For FOF slopes, make a special function to copy to the xy origin & direction relative to the position of the FOF on the map!
 	if(frontfloor || frontceil)
 	{
+		line->frontsector->hasslope = true; // Tell the software renderer that we're sloped
+
 		origin.z = line->backsector->floorheight;
 		direction.x = nx;
 		direction.y = ny;
@@ -327,6 +329,8 @@ void P_SpawnSlope_Line(int linenum)
 	}
 	if(backfloor || backceil)
 	{
+		line->backsector->hasslope = true; // Tell the software renderer that we're sloped
+
 		origin.z = line->frontsector->floorheight;
 		// Backsector
 		direction.x = -nx;
@@ -459,6 +463,8 @@ void P_CopySectorSlope(line_t *line)
          fsec->c_slope = srcsec->c_slope; //P_CopySlope(srcsec->c_slope);
    }
 
+   fsec->hasslope = true;
+
    line->special = 0; // Linedef was use to set slopes, it finished its job, so now make it a normal linedef
 }
 
diff --git a/src/r_bsp.c b/src/r_bsp.c
index 283029ca..8907ff42 100644
--- a/src/r_bsp.c
+++ b/src/r_bsp.c
@@ -946,6 +946,10 @@ static void R_Subsector(size_t num)
 
 #ifdef ESLOPE
 				ffloor[numffloors].slope = *rover->b_slope;
+
+				// Tell the renderer this sector has slopes in it.
+				if (ffloor[numffloors].slope)
+					frontsector->hasslope = true;
 #endif
 
 				ffloor[numffloors].height =
@@ -983,6 +987,10 @@ static void R_Subsector(size_t num)
 
 #ifdef ESLOPE
 				ffloor[numffloors].slope = *rover->t_slope;
+
+				// Tell the renderer this sector has slopes in it.
+				if (ffloor[numffloors].slope)
+					frontsector->hasslope = true;
 #endif
 
 				ffloor[numffloors].height =
diff --git a/src/r_defs.h b/src/r_defs.h
index b3667c05..b5b589e7 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -391,7 +391,9 @@ typedef struct sector_s
 	// Eternity engine slope
 	pslope_t *f_slope; // floor slope
 	pslope_t *c_slope; // ceiling slope
+	boolean hasslope; // The sector, or one of its visible FOFs, contains a slope
 #endif
+
 	// these are saved for netgames, so do not let Lua touch these!
 
 	// offsets sector spawned with (via linedef type 7)
diff --git a/src/r_segs.c b/src/r_segs.c
index 5d434b9a..a9d6c302 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -1602,7 +1602,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 	//  and decide if floor / ceiling marks are needed
 #ifdef ESLOPE
 	// Figure out map coordinates of where start and end are mapping to on seg, so we can clip right for slope bullshit
-	//if (frontsector->c_slope || frontsector->f_slope || (backsector && (backsector->c_slope || backsector->f_slope))) // Commenting this out for FOFslop. -Red
+	if (frontsector->hasslope || (backsector && backsector->hasslope)) // Commenting this out for FOFslop. -Red
 	{
 		angle_t temp;
 
@@ -2589,6 +2589,10 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 						continue;
 
 #ifdef ESLOPE
+					// Let the renderer know this sector is sloped.
+					if (*rover->b_slope || *rover->t_slope)
+						backsector->hasslope = true;
+
 					rovertest = (*rover->b_slope ? P_GetZAt(*rover->b_slope, segleft.x, segleft.y) : *rover->bottomheight) - viewz;
 					planevistest = (*rover->b_slope ? P_GetZAt(*rover->b_slope, viewx, viewy) : *rover->bottomheight);
 
@@ -2670,6 +2674,10 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 
 #ifdef ESLOPE
+					// Let the renderer know this sector is sloped.
+					if (*rover->b_slope || *rover->t_slope)
+						frontsector->hasslope = true;
+
 					rovertest = (*rover->b_slope ? P_GetZAt(*rover->b_slope, segleft.x, segleft.y) : *rover->bottomheight) - viewz;
 					planevistest = (*rover->b_slope ? P_GetZAt(*rover->b_slope, viewx, viewy) : *rover->bottomheight);