diff --git a/first/ackbuilder.lua b/first/ackbuilder.lua
index c7798e6b8..b59cb2a67 100644
--- a/first/ackbuilder.lua
+++ b/first/ackbuilder.lua
@@ -253,7 +253,7 @@ local function dirname(...)
 end
 
 local function replace(files, pattern, repl)
-	return dotocollection(files,
+	return dotocollection({files},
 		function(filename)
 			return filename:gsub(pattern, repl)
 		end