diff --git a/lib/ChunkMesher.lua b/lib/ChunkMesher.lua
index eb2dbb9..e9b4c39 100644
--- a/lib/ChunkMesher.lua
+++ b/lib/ChunkMesher.lua
@@ -64,6 +64,26 @@ end
 
 local ChunkMesher = {}
 
+-- Which drawn row a FLAT-topped volume's top face wears at depth `ty`.
+--
+-- A structure is usually deeper than the art that draws it, so the rows
+-- cycle and the drawing repeats down the top. That is right for art which
+-- genuinely repeats -- the Safari Zone's fence alternates two tiles the
+-- whole way down -- and wrong for a RIM over a uniform body: a cliff
+-- mound's first row is its top edge, and cycling lays that edge again
+-- every second tile, striping a plateau with rims it should not have.
+--
+-- Where Structures found the body uniform, the rim is laid once at the
+-- north edge and the body held after it. Everything else cycles as before.
+function ChunkMesher.flatTopRow(run, ty)
+  local m = math.min(2, run.extent)
+  local d = ty - run.north
+  if run.topUniform then
+    return run.north + math.min(d, m - 1)
+  end
+  return run.north + (d % m)
+end
+
 -- Ring of border blocks meshed around the body, matching the width
 -- TileRenderer draws so the two modes end at the same place.
 local RING = 3
@@ -528,8 +548,7 @@ local function runGeometry(map, bodyOnly, masks, sink, waterSink)
                  { x0 + 8, neY, z0 }, { x0, nwY, z0 } },
                { { u0, v1 }, { u1, v1 }, { u1, v0 }, { u0, v0 } }, 0.95)
         elseif run then
-          local m = math.min(2, run.extent)
-          local topTile = map:tileAt(tx, run.north + ((ty - run.north) % m))
+          local topTile = map:tileAt(tx, ChunkMesher.flatTopRow(run, ty))
           topQuad(x0, z0, h, topTile, VOLUME_TOP_SHADE)
         else
           local topTile = tile
diff --git a/lib/Structures.lua b/lib/Structures.lua
index 2c99c8d..8950380 100644
--- a/lib/Structures.lua
+++ b/lib/Structures.lua
@@ -2225,6 +2225,43 @@ function Structures.buildVolume(S, map, tiles)
   -- whether the region's dominant columns are flat repeats (a cliff
   -- mound's plateau) rather than drawn facades (a house's front)
   local modeRepeat = (repeatVotes[modeH] or 0) * 2 > modeN
+
+  -- Whether this REGION's tops are a rim over a uniform body -- what every
+  -- cliff mound is drawn as: a top edge, then the same rock the whole way
+  -- down. The top face may then lay that rim once along its north edge and
+  -- hold the body after it, instead of cycling the rim back every second
+  -- tile and striping a plateau with edges it should not have.
+  --
+  -- Answered per column AND per region, because each catches what the
+  -- other misses. A mound is one structure many columns wide, and the
+  -- columns carrying its cave mouth read differently from their neighbours
+  -- (their drawing ends in the mouth's own tiles): per column alone, those
+  -- kept cycling while the rest held, leaving rim stubs above the doorway.
+  -- But a region vote alone silences a genuine rim-over-body column that
+  -- happens to stand in a region of repeating art -- three of them in the
+  -- Safari Zone. A column holds if EITHER says so.
+  --
+  -- Art that genuinely repeats is not uniform and keeps cycling: the
+  -- Safari Zone's fence alternates two tiles the whole way down, and there
+  -- the repeat IS what the drawing says.
+  local uniformVotes, uniformTotal = 0, 0
+  for _, r in ipairs(runs) do
+    local run = r.run
+    if run.extent > 2 then
+      uniformTotal = uniformTotal + 1
+      local body = map:tileAt(r.tx, run.north + 1)
+      local uniform = true
+      for d = 2, run.extent - 1 do
+        if map:tileAt(r.tx, run.north + d) ~= body then
+          uniform = false
+          break
+        end
+      end
+      run.ownUniform = uniform
+      if uniform then uniformVotes = uniformVotes + 1 end
+    end
+  end
+  local regionUniform = uniformTotal > 0 and uniformVotes * 2 > uniformTotal
   for _, r in ipairs(runs) do
     local run = r.run
     local h = run.unit * 8
@@ -2272,6 +2309,7 @@ function Structures.buildVolume(S, map, tiles)
     run.rise = roofRows * 8
     run.peak = h
     run.h = h - run.rise               -- facade height: what sides build to
+    run.topUniform = run.ownUniform or regionUniform
     for ty = run.north, run.front do
       S.runs[keyOf(r.tx, ty)] = run
     end
diff --git a/tests/flat_top_test.lua b/tests/flat_top_test.lua
new file mode 100644
index 0000000..14035c0
--- /dev/null
+++ b/tests/flat_top_test.lua
@@ -0,0 +1,95 @@
+-- A flat top must not stamp its rim twice.
+--
+-- ChunkMesher.flatTopRow decides which drawn row a flat-topped volume's top
+-- face wears at each depth. Where the drawing is a RIM over a uniform body
+-- -- every cliff mound in the game, and the mound the Diglett's Cave mouth
+-- is cut into -- the rim belongs at the plateau's north edge and nowhere
+-- else. Cycling the first two rows lays it again every second tile.
+--
+-- The invariant: on such a run the sampled row never goes BACKWARDS as ty
+-- moves south. Art that genuinely repeats (the Safari Zone's fence
+-- alternates two tiles the whole way down) is exempt: there the repeat is
+-- what the drawing says, and the run is not rim-over-body.
+--
+--   POKEPORT_DRIVER=mods/DramaticShapeVoxelMod/tests/flat_top_test.lua lovec .
+return function(game)
+  local U = dofile("tests/drivers/util.lua")
+
+  local V = game.mods.exports["DRAMATIC_SHAPE"]
+  V = V and V.lib
+  local Structures = V and V.require("Structures")
+  local ChunkMesher = V and V.require("ChunkMesher")
+  if not (Structures and ChunkMesher and ChunkMesher.flatTopRow) then
+    print("[flattop] FAIL mod, Structures or ChunkMesher.flatTopRow missing")
+    love.event.quit(1)
+    return
+  end
+  local function keyOf(tx, ty) return (ty + 64) * 4096 + (tx + 64) end
+
+  local MAPS = {}
+  for id in pairs((game.data and game.data.maps) or {}) do
+    MAPS[#MAPS + 1] = id
+  end
+  table.sort(MAPS)
+
+  local checked, offenders, examples = 0, 0, {}
+  for _, mapId in ipairs(MAPS) do
+    U.teleport(game, mapId, 5, 5, "up")
+    U.wait(6)
+    local ow = game.overworld
+    if ow and ow.map and ow.map.def and ow.map.def.id == mapId then
+      local map = ow.map
+      local S = Structures.forMap(map)
+      local seen = {}
+      for tx = 0, map.def.width * 4 - 1 do
+        for ty = 0, map.def.height * 4 - 1 do
+          local run = S.runs[keyOf(tx, ty)]
+          local sig = run and (tostring(run) .. ":" .. tx)
+          if run and not seen[sig] and (run.rise or 0) == 0 then
+            seen[sig] = true
+            local ext = run.front - run.north + 1
+            -- rim over a uniform body: the shape the rim must not repeat on
+            local uniform = ext > 2
+            if uniform then
+              local body = map:tileAt(tx, run.north + 1)
+              for d = 2, ext - 1 do
+                if map:tileAt(tx, run.north + d) ~= body then
+                  uniform = false
+                  break
+                end
+              end
+            end
+            if uniform then
+              checked = checked + 1
+              local prev = -1
+              for ty2 = run.north, run.front do
+                local row = ChunkMesher.flatTopRow(run, ty2)
+                if row < prev then
+                  offenders = offenders + 1
+                  if #examples < 5 then
+                    examples[#examples + 1] = ("%s tx=%d north=%d ext=%d "
+                      .. "went back to row %d at ty %d")
+                      :format(mapId, tx, run.north, ext, row, ty2)
+                  end
+                  break
+                end
+                prev = row
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+
+  print(("[flattop] %d rim-over-body runs checked, %d repeat their rim")
+        :format(checked, offenders))
+  for _, e in ipairs(examples) do print("[flattop]   " .. e) end
+  if offenders > 0 then
+    print("[flattop] FAIL")
+    love.event.quit(1)
+  else
+    print("[flattop] PASS")
+    love.event.quit(0)
+  end
+end