diff --git a/c4mate b/c4mate
index d05fdcf..e827fb4 100755
--- a/c4mate
+++ b/c4mate
@@ -12,16 +12,16 @@ HOST = "http://mate.labor.koeln.ccc.de"
 local function utf8_decode(str)
     -- Replace JSON Unicode escape sequences with chars.
     if str == nil then return "" end
-    str = string.gsub(str, "\\\"", "\"")
+    str = str:gsub("\\\"", "\"")
     if utf8 == nil then return str end -- Only available in Lua >= 5.3.
-    return string.gsub(str, "\\u(%x%x%x%x)",
+    return str:gsub("\\u(%x%x%x%x)",
         function (s) return utf8.char(tonumber(s, 16)) end)
 end
 
 local function url_encode(str)
     -- URL-encode string. Used only for usernames.
     -- Todo: make this more sophisticated.
-    return string.gsub(str, " ", "%%20")
+    return str:gsub(" ", "%%20")
 end
 
 MatePad = {
@@ -421,12 +421,12 @@ else
     -- Find and buy item.
     local roster, query, input, ok
     roster = pad:get_roster()
-    query = string.lower(table.concat(arg, " "))
+    query = table.concat(arg, " "):lower()
     local menu = {}
 
     for i = 1, #roster do
         local item = roster[i]
-        if string.match(string.lower(item.name), query) then
+        if item.name:lower():match(query) then
             table.insert(menu, item)
         end
     end