diff --git a/dat/bigrm-3.lua b/dat/bigrm-3.lua
index e7c99a28a..ee7e0f310 100644
--- a/dat/bigrm-3.lua
+++ b/dat/bigrm-3.lua
@@ -30,6 +30,14 @@ des.map([[
 -- Dungeon Description
 des.region(selection.area(01,01,73,16), "lit");
 
+-- replace some walls
+if percent(66) then
+   local sel = selection.match("[.w.]");
+   local terrains = { "F", "T", "W", "Z" };
+   local choice = terrains[math.random(1, #terrains)];
+   des.terrain(sel, choice);
+end
+
 -- Stairs
 des.stair("up");
 des.stair("down");
diff --git a/doc/fixes3-7-0.txt b/doc/fixes3-7-0.txt
index 412bd333e..74b821885 100644
--- a/doc/fixes3-7-0.txt
+++ b/doc/fixes3-7-0.txt
@@ -976,6 +976,7 @@ wielding a bec de corbin makes ravens generate peaceful
 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 3 may have some walls replaced with other terrain
 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