diff --git a/src/dehacked.c b/src/dehacked.c
index c6cd0b9e5..20d23d680 100644
--- a/src/dehacked.c
+++ b/src/dehacked.c
@@ -9648,11 +9648,11 @@ struct {
 	{"FF_CUTEXTRA",FF_CUTEXTRA},               ///< Cuts out hidden translucent pixels.
 	{"FF_CUTLEVEL",FF_CUTLEVEL},               ///< Cuts out all hidden pixels.
 	{"FF_CUTSPRITES",FF_CUTSPRITES},           ///< Final step in making 3D water.
-	{"FF_BOTHPLANES",FF_BOTHPLANES},           ///< Renders both planes all the time.
+	{"FF_BOTHPLANES",FF_BOTHPLANES},           ///< Render inside and outside planes.
 	{"FF_EXTRA",FF_EXTRA},                     ///< Gets cut by ::FF_CUTEXTRA.
 	{"FF_TRANSLUCENT",FF_TRANSLUCENT},         ///< See through!
 	{"FF_FOG",FF_FOG},                         ///< Fog "brush."
-	{"FF_INVERTPLANES",FF_INVERTPLANES},       ///< Reverse the plane visibility rules.
+	{"FF_INVERTPLANES",FF_INVERTPLANES},       ///< Only render inside planes.
 	{"FF_ALLSIDES",FF_ALLSIDES},               ///< Render inside and outside sides.
 	{"FF_INVERTSIDES",FF_INVERTSIDES},         ///< Only render inside sides.
 	{"FF_DOUBLESHADOW",FF_DOUBLESHADOW},       ///< Make two lightlist entries to reset light?
diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index c56f0ec06..51c6471ac 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -1902,7 +1902,9 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 		{
 			for (rover = gr_backsector->ffloors; rover; rover = rover->next)
 			{
-				if (!(rover->flags & FF_EXISTS) || !(rover->flags & FF_RENDERSIDES) || (rover->flags & FF_INVERTSIDES))
+				if (!(rover->flags & FF_EXISTS) || !(rover->flags & FF_RENDERSIDES))
+					continue;
+				if (!(rover->flags & FF_ALLSIDES) && rover->flags & FF_INVERTSIDES)
 					continue;
 				if (*rover->topheight < lowcut || *rover->bottomheight > highcut)
 					continue;
@@ -2042,7 +2044,9 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 		{
 			for (rover = gr_frontsector->ffloors; rover; rover = rover->next)
 			{
-				if (!(rover->flags & FF_EXISTS) || !(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_ALLSIDES))
+				if (!(rover->flags & FF_EXISTS) || !(rover->flags & FF_RENDERSIDES))
+					continue;
+				if (!(rover->flags & FF_ALLSIDES || rover->flags & FF_INVERTSIDES))
 					continue;
 				if (*rover->topheight < lowcut || *rover->bottomheight > highcut)
 					continue;
@@ -3427,7 +3431,7 @@ static void HWR_Subsector(size_t num)
 
 			if (centerHeight <= locCeilingHeight &&
 			    centerHeight >= locFloorHeight &&
-			    ((dup_viewz < cullHeight && !(rover->flags & FF_INVERTPLANES)) ||
+			    ((dup_viewz < cullHeight && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
 			     (dup_viewz > cullHeight && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 			{
 				if (rover->flags & FF_FOG)
@@ -3488,7 +3492,7 @@ static void HWR_Subsector(size_t num)
 
 			if (centerHeight >= locFloorHeight &&
 			    centerHeight <= locCeilingHeight &&
-			    ((dup_viewz > cullHeight && !(rover->flags & FF_INVERTPLANES)) ||
+			    ((dup_viewz > cullHeight && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
 			     (dup_viewz < cullHeight && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 			{
 				if (rover->flags & FF_FOG)
diff --git a/src/p_sight.c b/src/p_sight.c
index c9083b99b..3d1ee9e60 100644
--- a/src/p_sight.c
+++ b/src/p_sight.c
@@ -495,7 +495,7 @@ boolean P_CheckSight(mobj_t *t1, mobj_t *t2)
 			if (rover->flags & FF_SOLID)
 				continue; // shortcut since neither mobj can be inside the 3dfloor
 
-			if (!(rover->flags & FF_INVERTPLANES))
+			if (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))
 			{
 				if (los.sightzstart >= topz1 && t2->z + t2->height < topz2)
 					return false; // blocked by upper outside plane
@@ -504,7 +504,7 @@ boolean P_CheckSight(mobj_t *t1, mobj_t *t2)
 					return false; // blocked by lower outside plane
 			}
 
-			if (rover->flags & FF_INVERTPLANES || rover->flags & FF_BOTHPLANES)
+			if (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES)
 			{
 				if (los.sightzstart < topz1 && t2->z >= topz2)
 					return false; // blocked by upper inside plane
diff --git a/src/p_spec.c b/src/p_spec.c
index cd26dcf9e..dee816e47 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -7069,7 +7069,7 @@ void P_SpawnSpecials(boolean fromnetsave)
 				break;
 
 			case 202: // Fog
-				ffloorflags = FF_EXISTS|FF_RENDERALL|FF_FOG|FF_BOTHPLANES|FF_INVERTPLANES|FF_ALLSIDES|FF_INVERTSIDES|FF_CUTEXTRA|FF_EXTRA|FF_DOUBLESHADOW|FF_CUTSPRITES;
+				ffloorflags = FF_EXISTS|FF_RENDERALL|FF_FOG|FF_INVERTPLANES|FF_INVERTSIDES|FF_CUTEXTRA|FF_EXTRA|FF_DOUBLESHADOW|FF_CUTSPRITES;
 				sec = sides[*lines[i].sidenum].sector - sectors;
 				// SoM: Because it's fog, check for an extra colormap and set the fog flag...
 				if (sectors[sec].extra_colormap)
diff --git a/src/r_bsp.c b/src/r_bsp.c
index 85113be43..77ab2a82f 100644
--- a/src/r_bsp.c
+++ b/src/r_bsp.c
@@ -955,8 +955,8 @@ static void R_Subsector(size_t num)
 				*rover->bottomheight;
 			if (planecenterz <= ceilingcenterz
 				&& planecenterz >= floorcenterz
-				&& ((viewz < heightcheck && !(rover->flags & FF_INVERTPLANES))
-				|| (viewz > heightcheck && (rover->flags & FF_BOTHPLANES))))
+				&& ((viewz < heightcheck && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES)))
+				|| (viewz > heightcheck && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 			{
 				light = R_GetPlaneLight(frontsector, planecenterz,
 					viewz < heightcheck);
@@ -993,8 +993,8 @@ static void R_Subsector(size_t num)
 				*rover->topheight;
 			if (planecenterz >= floorcenterz
 				&& planecenterz <= ceilingcenterz
-				&& ((viewz > heightcheck && !(rover->flags & FF_INVERTPLANES))
-				|| (viewz < heightcheck && (rover->flags & FF_BOTHPLANES))))
+				&& ((viewz > heightcheck && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES)))
+				|| (viewz < heightcheck && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 			{
 				light = R_GetPlaneLight(frontsector, planecenterz, viewz < heightcheck);
 
diff --git a/src/r_defs.h b/src/r_defs.h
index 0c6ff1d30..5f62ec058 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -130,11 +130,11 @@ typedef enum
 	FF_CUTEXTRA          = 0x100,      ///< Cuts out hidden translucent pixels.
 	FF_CUTLEVEL          = 0x180,      ///< Cuts out all hidden pixels.
 	FF_CUTSPRITES        = 0x200,      ///< Final step in making 3D water.
-	FF_BOTHPLANES        = 0x400,      ///< Renders both planes all the time.
+	FF_BOTHPLANES        = 0x400,      ///< Render inside and outside planes.
 	FF_EXTRA             = 0x800,      ///< Gets cut by ::FF_CUTEXTRA.
 	FF_TRANSLUCENT       = 0x1000,     ///< See through!
 	FF_FOG               = 0x2000,     ///< Fog "brush."
-	FF_INVERTPLANES      = 0x4000,     ///< Reverse the plane visibility rules.
+	FF_INVERTPLANES      = 0x4000,     ///< Only render inside planes.
 	FF_ALLSIDES          = 0x8000,     ///< Render inside and outside sides.
 	FF_INVERTSIDES       = 0x10000,    ///< Only render inside sides.
 	FF_DOUBLESHADOW      = 0x20000,    ///< Make two lightlist entries to reset light?
diff --git a/src/r_segs.c b/src/r_segs.c
index d8f1981ee..d4b07ff13 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -2165,7 +2165,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 				{
 					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS))
 						continue;
-					if (rover->flags & FF_INVERTSIDES)
+					if (!(rover->flags & FF_ALLSIDES) && rover->flags & FF_INVERTSIDES)
 						continue;
 
 					if (rover->norender == leveltime)
@@ -2220,7 +2220,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 				{
 					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS))
 						continue;
-					if (!(rover->flags & FF_ALLSIDES))
+					if (!(rover->flags & FF_ALLSIDES || rover->flags & FF_INVERTSIDES))
 						continue;
 
 					if (rover->norender == leveltime)
@@ -2275,7 +2275,9 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			{
 				for (rover = backsector->ffloors, i = 0; rover && i < MAXFFLOORS; rover = rover->next)
 				{
-					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS) || rover->flags & FF_INVERTSIDES)
+					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS))
+						continue;
+					if (!(rover->flags & FF_ALLSIDES) && rover->flags & FF_INVERTSIDES)
 						continue;
 					if (rover->norender == leveltime)
 						continue;
@@ -2295,7 +2297,9 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			{
 				for (rover = frontsector->ffloors, i = 0; rover && i < MAXFFLOORS; rover = rover->next)
 				{
-					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS) || !(rover->flags & FF_ALLSIDES))
+					if (!(rover->flags & FF_RENDERSIDES) || !(rover->flags & FF_EXISTS))
+						continue;
+					if (!(rover->flags & FF_ALLSIDES || rover->flags & FF_INVERTSIDES))
 						continue;
 					if (rover->norender == leveltime)
 						continue;
@@ -2620,8 +2624,8 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 					if ((roverleft>>4 <= worldhigh || roverright>>4 <= worldhighslope) &&
 					    (roverleft>>4 >= worldlow || roverright>>4 >= worldlowslope) &&
-					    ((viewz < planevistest && !(rover->flags & FF_INVERTPLANES)) ||
-					     (viewz > planevistest && (rover->flags & FF_BOTHPLANES))))
+					    ((viewz < planevistest && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
+					     (viewz > planevistest && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 					{
 						//ffloor[i].slope = *rover->b_slope;
 						ffloor[i].b_pos = roverleft;
@@ -2643,8 +2647,8 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 					if ((roverleft>>4 <= worldhigh || roverright>>4 <= worldhighslope) &&
 					    (roverleft>>4 >= worldlow || roverright>>4 >= worldlowslope) &&
-					    ((viewz > planevistest && !(rover->flags & FF_INVERTPLANES)) ||
-					     (viewz < planevistest && (rover->flags & FF_BOTHPLANES))))
+					    ((viewz > planevistest && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
+					     (viewz < planevistest && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 					{
 						//ffloor[i].slope = *rover->t_slope;
 						ffloor[i].b_pos = roverleft;
@@ -2677,8 +2681,8 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 					if ((roverleft>>4 <= worldhigh || roverright>>4 <= worldhighslope) &&
 					    (roverleft>>4 >= worldlow || roverright>>4 >= worldlowslope) &&
-					    ((viewz < planevistest && !(rover->flags & FF_INVERTPLANES)) ||
-					     (viewz > planevistest && (rover->flags & FF_BOTHPLANES))))
+					    ((viewz < planevistest && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
+					     (viewz > planevistest && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 					{
 						//ffloor[i].slope = *rover->b_slope;
 						ffloor[i].b_pos = roverleft;
@@ -2700,8 +2704,8 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 					if ((roverleft>>4 <= worldhigh || roverright>>4 <= worldhighslope) &&
 					    (roverleft>>4 >= worldlow || roverright>>4 >= worldlowslope) &&
-					    ((viewz > planevistest && !(rover->flags & FF_INVERTPLANES)) ||
-					     (viewz < planevistest && (rover->flags & FF_BOTHPLANES))))
+					    ((viewz > planevistest && (rover->flags & FF_BOTHPLANES || !(rover->flags & FF_INVERTPLANES))) ||
+					     (viewz < planevistest && (rover->flags & FF_BOTHPLANES || rover->flags & FF_INVERTPLANES))))
 					{
 						//ffloor[i].slope = *rover->t_slope;
 						ffloor[i].b_pos = roverleft;