diff --git a/Rakefile b/Rakefile
index ec6ed32bd..0088a2e2a 100644
--- a/Rakefile
+++ b/Rakefile
@@ -163,6 +163,7 @@ op_table = {
 file presym_file => cfiles+rbfiles+psfiles+[__FILE__] do
   csymbols = cfiles.map do |f|
     src = File.read(f)
+    src.gsub!(/\/\/.+(\n|$)/, "\n")
     [src.scan(/intern_lit\([^\n"]*"([^\n "]*)"/),
      src.scan(/mrb_define_method\([^\n"]*"([^\n"]*)"/),
      src.scan(/mrb_define_class_method\([^\n"]*"([^\n"]*)"/),