diff --git a/Source/r_segs.c b/Source/r_segs.c
index 64760f8d..d87bc5f1 100644
--- a/Source/r_segs.c
+++ b/Source/r_segs.c
@@ -208,6 +208,8 @@ void R_RenderMaskedSegRange(drawseg_t *ds, int x1, int x2)
 
   // Except for main_tranmap, mark others purgable at this point
   if (curline->linedef->tranlump > 0 && general_translucency)
+   // [FG] make sure to never mark main_tranmap as purgeable
+   if (tranmap != main_tranmap)
     Z_ChangeTag(tranmap, PU_CACHE); // killough 4/11/98
 }