diff --git a/clean-k-tags.lua b/clean-k-tags.lua
index 2b7de39..c1daf07 100644
--- a/clean-k-tags.lua
+++ b/clean-k-tags.lua
@@ -5,26 +5,39 @@ script_description = tr"Remove double k tags"
 script_author = "amoethyst"
 script_version = "1.0"
 
+local double_k = "^(.-{\\k[^}]-)(\\k.+)$"
+-- if the first tag is K/kf this would break the timing for the previous timing
+local expr = "^(.-){\\(ko?)([0-9.]+)[^}]-}([^{]-){\\[kK][fo]?([0-9.]+)[^}]-}( -{(\\[kK][fo]?)[0-9.]+[^}]-}.*)$"
+
+
+function _special_k(subs, i)
+    line = subs[i]
+
+    before, after = line.text:match(double_k)
+    while after ~= nil do
+        line.text = before .. "}{" .. after
+        before, after = line.text:match(double_k)
+    end
+
+    before, tag, k1, between, k2, after = line.text:match(expr)
+    while after ~= nil do
+        line.text = before .. "{\\" .. tag .. tonumber(k1) + tonumber(k2) .. "}" .. between .. after
+        before, tag, k1, between, k2, after = line.text:match(expr)
+    end
+
+    return line
+end
+
+
 function special_k(subs, sel)
 
-    local double_k = "^(.-{\\k[^}]-)(\\k.+)$"
-    -- if the first tag is K/kf this would break the timing for the previous timing
-    local expr = "^(.-){\\(ko?)([0-9.]+)[^}]-}([^{]-){\\[kK][fo]?([0-9.]+)[^}]-}( -{(\\[kK][fo]?)[0-9.]+[^}]-}.*)$"
-
     for _, i in ipairs(sel) do
-        line = subs[i]
-
-        before, after = line.text:match(double_k)
-        while after ~= nil do
-            line.text = before .. "}{" .. after
-            before, after = line.text:match(double_k)
-        end
-
-        before, tag, k1, between, k2, after = line.text:match(expr)
-        while after ~= nil do
-            line.text = before .. "{\\" .. tag .. tonumber(k1) + tonumber(k2) .. "}" .. between .. after
-            subs[i] = line
-            before, tag, k1, between, k2, after = line.text:match(expr)
+        ok, res = pcall(_special_k, subs, i)
+        if ok then
+            subs[i] = res
+        else
+            aegisub.log("error on line " .. i .. ": " .. line.text .. "\n")
+            aegisub.log(res .. "\n")
         end
     end