diff --git a/macros/garret.dupe-and-comment.lua b/macros/garret.dupe-and-comment.lua
index f8e4b4b..f819d40 100644
--- a/macros/garret.dupe-and-comment.lua
+++ b/macros/garret.dupe-and-comment.lua
@@ -13,11 +13,20 @@ end
 
 local function comment(subs, sel, act)
     for i=#sel,1,-1 do
-        local line=subs[sel[i]]
-        line.comment = true
-        subs.insert(sel[i]+1, line)
-        for j=i+1,#sel do sel[j] = sel[j] + 1 end
-        if act > sel[i] then act = act + 1 end
+        local line=subs[sel[i]] -- grab copy of current line
+
+        -- now use that copy for a different line
+        line.comment = true -- comment out the new dupe line
+        subs.insert(sel[i]+1, line) -- and put it below
+
+        -- sort out selection
+        for j=i+1,#sel do
+            sel[j] = sel[j] + 1 -- bump all of sel by 1 to compensate for new line
+        end -- first item isnt included because it's not affected
+
+        if act > sel[i] then -- if we've not got to the active line yet
+            act = act + 1 -- bump by 1 to compensate for new lines above
+        end
     end
     aegisub.set_undo_point(script_name)
     return sel, act