diff --git a/src/g_game.c b/src/g_game.c
index c05d7f78..9b761763 100644
--- a/src/g_game.c
+++ b/src/g_game.c
@@ -950,8 +950,6 @@ static void G_DoLoadLevel(void)
         break;
       }//jff 3/27/98 end sky setting fix
 
-  R_InitSkyMap(); // [FG] stretch short skies
-
   levelstarttic = gametic;        // for time calculation
 
   playback_levelstarttic = playback_tic;
@@ -993,6 +991,8 @@ static void G_DoLoadLevel(void)
   MN_UpdateFreeLook(!mouselook && !padlook);
   HU_UpdateTurnFormat();
 
+  R_InitSkyMap(); // SKYDEFS flatmapping
+
   // [Woof!] Do not reset chosen player view across levels in multiplayer
   // demo playback. However, it must be reset when starting a new game.
   if (usergame)
diff --git a/src/p_setup.c b/src/p_setup.c
index 9e0e516a..9a905126 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -345,7 +345,7 @@ void P_LoadSectors (int lump)
       ss->bottommap = ss->midmap = ss->topmap = 0;
 
       // killough 10/98: sky textures coming from sidedefs:
-      ss->sky = 0;
+      ss->floorsky = ss->ceilingsky = 0;
 
       // [AM] Sector interpolation.  Even if we're
       //      not running uncapped, the renderer still
diff --git a/src/p_spec.c b/src/p_spec.c
index 3c21978e..34be90c2 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -2630,7 +2630,7 @@ void P_SpawnSpecials (void)
         // Pre-calculate sky color
         R_GetSkyColor(texturetranslation[sides[*lines[i].sidenum].toptexture]);
         for (s = -1; (s = P_FindSectorFromLineTag(lines+i,s)) >= 0;)
-          sectors[s].sky = i | PL_SKYFLAT;
+          sectors[s].floorsky = sectors[s].ceilingsky = i | PL_SKYFLAT;
         break;
       }
 }
diff --git a/src/r_bsp.c b/src/r_bsp.c
index 99c5be83..645e28e4 100644
--- a/src/r_bsp.c
+++ b/src/r_bsp.c
@@ -616,7 +616,7 @@ static void R_Subsector(int num)
      sectors[frontsector->heightsec].ceilingpic == skyflatnum) ?
     R_FindPlane(frontsector->interpfloorheight,
 		frontsector->floorpic == skyflatnum &&  // kilough 10/98
-		frontsector->sky & PL_SKYFLAT ? frontsector->sky :
+		frontsector->floorsky & PL_SKYFLAT ? frontsector->floorsky :
                 frontsector->floorpic,
                 floorlightlevel,                // killough 3/16/98
                 frontsector->floor_xoffs,       // killough 3/7/98
@@ -629,7 +629,7 @@ static void R_Subsector(int num)
      sectors[frontsector->heightsec].floorpic == skyflatnum) ?
     R_FindPlane(frontsector->interpceilingheight,     // killough 3/8/98
 		frontsector->ceilingpic == skyflatnum &&  // kilough 10/98
-		frontsector->sky & PL_SKYFLAT ? frontsector->sky :
+		frontsector->ceilingsky & PL_SKYFLAT ? frontsector->ceilingsky :
                 frontsector->ceilingpic,
                 ceilinglightlevel,              // killough 4/11/98
                 frontsector->ceiling_xoffs,     // killough 3/7/98
diff --git a/src/r_defs.h b/src/r_defs.h
index 605c0a5f..612d18c6 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -125,7 +125,7 @@ typedef struct sector_s
   // or ceilingpic, because the rest of Doom needs to know which is sky
   // and which isn't, etc.
 
- int sky;
+ int floorsky, ceilingsky;
 
   // list of mobjs that are at least partially in the sector
   // thinglist is a subset of touching_thinglist
diff --git a/src/r_plane.c b/src/r_plane.c
index 77136220..04d1c10d 100644
--- a/src/r_plane.c
+++ b/src/r_plane.c
@@ -488,7 +488,13 @@ static void do_draw_mbf_sky(visplane_t *pl)
 
     an = viewangle;
 
-    if (pl->picnum & PL_SKYFLAT)
+    if ((pl->picnum & PL_FLATMAPPING) == PL_FLATMAPPING)
+    {
+        dc_texturemid = skytexturemid;
+        texture = pl->picnum & ~PL_FLATMAPPING;
+        flip = 0;
+    }
+    else if (pl->picnum & PL_SKYFLAT)
     {
         // Sky Linedef
         const line_t *l = &lines[pl->picnum & ~PL_SKYFLAT];
@@ -601,10 +607,19 @@ static void do_draw_plane(visplane_t *pl)
 
     // sky flat
 
-    if (pl->picnum == skyflatnum && sky)
+    if (sky)
     {
-        DrawSkyDef(pl);
-        return;
+        if ((pl->picnum & PL_FLATMAPPING) == PL_FLATMAPPING)
+        {
+            do_draw_mbf_sky(pl);
+            return;
+        }
+
+        if (pl->picnum == skyflatnum)
+        {
+            DrawSkyDef(pl);
+            return;
+        }
     }
 
     if (pl->picnum == skyflatnum || pl->picnum & PL_SKYFLAT)
diff --git a/src/r_sky.c b/src/r_sky.c
index 908bbc04..ae0297cc 100644
--- a/src/r_sky.c
+++ b/src/r_sky.c
@@ -137,6 +137,29 @@ static void InitSky(void)
         return;
     }
 
+    flatmap_t *flatmap = NULL;
+    array_foreach(flatmap, skydefs->flatmapping)
+    {
+        int flatnum = R_FlatNumForName(flatmap->flat);
+        int skytex = R_TextureNumForName(flatmap->sky);
+
+        for (int i = 0; i < numsectors; i++)
+        {
+            if (sectors[i].floorpic == flatnum)
+            {
+                sectors[i].floorpic = skyflatnum;
+                sectors[i].floorsky = skytex | PL_FLATMAPPING;
+                R_GetSkyColor(skytex);
+            }
+            if (sectors[i].ceilingpic == flatnum)
+            {
+                sectors[i].ceilingpic = skyflatnum;
+                sectors[i].ceilingsky = skytex | PL_FLATMAPPING;
+                R_GetSkyColor(skytex);
+            }
+        }
+    }
+
     array_foreach(sky, skydefs->skies)
     {
         if (skytexture == R_CheckTextureNumForName(sky->skytex.name))
diff --git a/src/r_sky.h b/src/r_sky.h
index a4491af9..138e7638 100644
--- a/src/r_sky.h
+++ b/src/r_sky.h
@@ -39,6 +39,8 @@ extern boolean linearsky;
 extern int skytexture;
 extern int skytexturemid;
 
+#define PL_FLATMAPPING (0xC0000000) // (PL_SKYFLAT | 0x40000000)
+
 extern sky_t *sky;
 
 // Called whenever the view size changes.