diff --git a/docs/changelog.txt b/docs/changelog.txt
index fba342802..3363a6c77 100644
--- a/docs/changelog.txt
+++ b/docs/changelog.txt
@@ -33,6 +33,9 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 
 # Future
 
+## Fixes
+- `buildingplan`: fixed an issue where planned constructions designated with DF's sizing keys (``umkh``) would sometimes be larger than requested
+
 ## Lua
 - ``gui.Painter``: fixed error when calling ``viewport()`` method
 - `xlsxreader`: Added Lua class wrappers for the xlsxreader plugin API
diff --git a/plugins/lua/buildingplan.lua b/plugins/lua/buildingplan.lua
index c0e69168a..43122a7da 100644
--- a/plugins/lua/buildingplan.lua
+++ b/plugins/lua/buildingplan.lua
@@ -103,9 +103,9 @@ function construct_buildings_from_ui_state()
     if width == 1 and height == 1 and
             (world.building_width > 1 or world.building_height > 1) then
         min_x = math.ceil(pos.x - world.building_width/2)
-        max_x = math.floor(pos.x + world.building_width/2)
+        max_x = min_x + world.building_width - 1
         min_y = math.ceil(pos.y - world.building_height/2)
-        max_y = math.floor(pos.y + world.building_height/2)
+        max_y = min_y + world.building_height - 1
     end
     local blds = {}
     for y=min_y,max_y do for x=min_x,max_x do