diff --git a/gui/design.lua b/gui/design.lua
index 7c27aaf1fd..0005263944 100644
--- a/gui/design.lua
+++ b/gui/design.lua
@@ -1795,14 +1795,18 @@ DimensionsOverlay.ATTRS{
 local selection_rect = df.global.selection_rect
 
 local function is_choosing_area()
-    return selection_rect.start_x >= 0 and dfhack.gui.getMousePos()
+    return selection_rect.start_z >= 0 and dfhack.gui.getMousePos(true)
 end
 
 local function get_cur_area_dims()
-    local pos1 = dfhack.gui.getMousePos()
-    if not pos1 or selection_rect.start_x < 0 then return 1, 1, 1 end
+    local pos1 = dfhack.gui.getMousePos(true)
+    if not pos1 or selection_rect.start_z < 0 then return 1, 1, 1 end
 
     -- clamp to map edges (since you can start selection out of bounds)
+    pos1 = xyz2pos(
+        math.max(0, math.min(df.global.world.map.x_count-1, pos1.x)),
+        math.max(0, math.min(df.global.world.map.y_count-1, pos1.y)),
+        math.max(0, math.min(df.global.world.map.z_count-1, pos1.z)))
     local pos2 = xyz2pos(
         math.max(0, math.min(df.global.world.map.x_count-1, selection_rect.start_x)),
         math.max(0, math.min(df.global.world.map.y_count-1, selection_rect.start_y)),