diff --git a/dat/bigrm-5.lua b/dat/bigrm-5.lua
index dae30fd5d..3e40812e6 100644
--- a/dat/bigrm-5.lua
+++ b/dat/bigrm-5.lua
@@ -28,6 +28,12 @@ des.map([[
                             ------------------                            
 ]]);
 
+
+if percent(25) then
+   local sel = selection.match("."):percentage(2):grow();
+   des.replace_terrain({ selection=sel, fromterrain=".", toterrain=percent(50) and "I" or "C" });
+end
+
 des.region(selection.area(00,00,72,18), "lit");
 
 des.stair("up");
diff --git a/doc/fixes3-7-0.txt b/doc/fixes3-7-0.txt
index 163b3893a..61018d800 100644
--- a/doc/fixes3-7-0.txt
+++ b/doc/fixes3-7-0.txt
@@ -977,6 +977,7 @@ moving with 'm' prefix allows hero to enter a known pit carefully
 rangers always succeed in disarming bear traps, unless impaired
 bigroom variant 2 may have ice floor in unlit areas
 bigroom variant 4 may have two large squares of terrain in the middle
+bigroom variant 5 may have patches of ice or clouds
 some large monsters can knock back smaller monsters with a hit
 change Demonbane to a mace, make it the first sac gift for priests,
 	and give it an invoke ability to banish demons