diff --git a/src/main.lua b/src/main.lua
index bcd17cc..fd230f5 100644
--- a/src/main.lua
+++ b/src/main.lua
@@ -93,7 +93,7 @@ local function newdesign()
 
         -- user input
         local event = table.pack(os.pullEvent())
-        if event[1] == "mouse_click" then
+        if (event[1] == "mouse_click" or event[1] == "mouse_drag") and event[3] > 0 and event[3] <= dimensions["x"] and event[4] > 0 and event[4] <= dimensions["z"] then
             if event[2] == 1 then -- left button, set
                 buf[posasstring(event[3], currentfloor, event[4])] = true
             end