diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index 967758eab..f03b0c342 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -449,6 +449,7 @@ static void R_AddLine(seg_t *line)
 {
 	INT32 x1, x2;
 	angle_t angle1, angle2, span, tspan;
+	static sector_t tempsec;
 	boolean bothceilingssky = false, bothfloorssky = false;
 
 	g_portal = NULL;
@@ -544,6 +545,8 @@ static void R_AddLine(seg_t *line)
 		goto clipsolid;
 	}
 
+	backsector = R_FakeFlat(backsector, &tempsec, NULL, NULL, true);
+
 	doorclosed = 0;
 
 	if (mapnamespace != MNS_SRB2KART)