diff --git a/pixler.bas b/pixler.bas
index 70a149a..3c6f827 100644
--- a/pixler.bas
+++ b/pixler.bas
@@ -602,12 +602,32 @@ sub do.fcircle (sx as long,sy as long,ex as long,ey as long,col as long)
     end if
 end sub
 
-sub do.box(sx as long,sy as long,ex as long,ey as long,col as long)
+sub do.box (sx as long,sy as long,ex as long,ey as long,col as long)
     dim osource as long
     dim odest as long
+    
     if state.isdrawing then
         osource=_source
         odest=_dest
+        
+        ' --- Shift Held: Perfect Square Constraint ---
+        if _keydown(100303) or _keydown(100304) then
+            dim dx as long: dx = ex - sx
+            dim dy as long: dy = ey - sy
+            
+            ' Determine the longest side to use as the square dimensions
+            dim size as long
+            if abs(dx) > abs(dy) then size = abs(dx) else size = abs(dy)
+            
+            ' Shift coordinates relative to the direction of the drag
+            dim signx as long: if dx >= 0 then signx = 1 else signx = -1
+            dim signy as long: if dy >= 0 then signy = 1 else signy = -1
+            
+            ex = sx + (size * signx)
+            ey = sy + (size * signy)
+        end if
+        ' ---------------------------------------------
+
         if mouseclicked or rmouseclicked then
             _dest layers(1).ihandle
             addcommand"box ("+tst(sx)+","+tst(sy)+","+tst(ex)+","+tst(ey)+","+hex$(col)+")"
@@ -621,12 +641,32 @@ sub do.box(sx as long,sy as long,ex as long,ey as long,col as long)
     end if
 end sub
 
-sub do.fbox(sx as long,sy as long,ex as long,ey as long,col as long)
+sub do.fbox (sx as long,sy as long,ex as long,ey as long,col as long)
     dim osource as long
     dim odest as long
+    
     if state.isdrawing then
         osource=_source
         odest=_dest
+        
+        ' --- Shift Held: Perfect Square Constraint ---
+        if _keydown(100303) or _keydown(100304) then
+            dim dx as long: dx = ex - sx
+            dim dy as long: dy = ey - sy
+            
+            ' Determine the longest side to use as the square dimensions
+            dim size as long
+            if abs(dx) > abs(dy) then size = abs(dx) else size = abs(dy)
+            
+            ' Shift coordinates relative to the direction of the drag
+            dim signx as long: if dx >= 0 then signx = 1 else signx = -1
+            dim signy as long: if dy >= 0 then signy = 1 else signy = -1
+            
+            ex = sx + (size * signx)
+            ey = sy + (size * signy)
+        end if
+        ' ---------------------------------------------
+
         if mouseclicked or rmouseclicked then
             _dest layers(1).ihandle
             addcommand"fbox ("+tst(sx)+","+tst(sy)+","+tst(ex)+","+tst(ey)+","+hex$(col)+")"