diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index b7675a21b..01cc9b01f 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -2023,7 +2023,7 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 		// Single sided line... Deal only with the middletexture (if one exists)
 		gr_midtexture = R_GetTextureNum(gr_sidedef->midtexture);
 		if (gr_midtexture
-			&& gr_linedef->special != 41) // Ignore horizon line for OGL
+			&& gr_linedef->special != HORIZONSPECIAL) // Ignore horizon line for OGL
 		{
 			{
 				fixed_t     texturevpeg;
diff --git a/src/r_defs.h b/src/r_defs.h
index 52a3be80e..c8a72044d 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -406,6 +406,8 @@ typedef enum
 	ST_NEGATIVE
 } slopetype_t;
 
+#define HORIZONSPECIAL 41
+
 typedef struct line_s
 {
 	// Vertices, from v1 to v2.
diff --git a/src/r_segs.c b/src/r_segs.c
index 399f514bc..2304540fe 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -2687,7 +2687,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 	worldbottomslope >>= 4;
 #endif
 
-	if (linedef->special == 41) { // HORIZON LINES
+	if (linedef->special == HORIZONSPECIAL) { // HORIZON LINES
 		topstep = bottomstep = 0;
 		topfrac = bottomfrac = (centeryfrac>>4);
 		topfrac++; // Prevent 1px HOM
@@ -2817,12 +2817,23 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			ffloor[i].f_pos >>= 4;
 #ifdef ESLOPE
 			ffloor[i].f_pos_slope >>= 4;
-			ffloor[i].f_frac = (centeryfrac>>4) - FixedMul(ffloor[i].f_pos, rw_scale);
-			ffloor[i].f_step = ((centeryfrac>>4) - FixedMul(ffloor[i].f_pos_slope, ds_p->scale2) - ffloor[i].f_frac)/(range);
-#else
-			ffloor[i].f_step = FixedMul(-rw_scalestep, ffloor[i].f_pos);
-			ffloor[i].f_frac = (centeryfrac>>4) - FixedMul(ffloor[i].f_pos, rw_scale);
 #endif
+			if (linedef->special == HORIZONSPECIAL) // Horizon lines extend FOFs in contact with them too.
+			{
+				ffloor[i].f_step = 0;
+				ffloor[i].f_frac = (centeryfrac>>4);
+				topfrac++; // Prevent 1px HOM
+			}
+			else
+			{
+#ifdef ESLOPE
+				ffloor[i].f_frac = (centeryfrac>>4) - FixedMul(ffloor[i].f_pos, rw_scale);
+				ffloor[i].f_step = ((centeryfrac>>4) - FixedMul(ffloor[i].f_pos_slope, ds_p->scale2) - ffloor[i].f_frac)/(range);
+#else
+				ffloor[i].f_step = FixedMul(-rw_scalestep, ffloor[i].f_pos);
+				ffloor[i].f_frac = (centeryfrac>>4) - FixedMul(ffloor[i].f_pos, rw_scale);
+#endif
+			}
 		}
 	}