diff --git a/script/check_contributors_md b/script/check_contributors_md
index 131daf445..d108ca56c 100755
--- a/script/check_contributors_md
+++ b/script/check_contributors_md
@@ -28,7 +28,7 @@ Please set it using
   end
 end
 
-if !system("grep #{author} CONTRIBUTORS.md") then
+unless system('grep', '-i', author, 'CONTRIBUTORS.md') then
   abort %{
 Thanks for your contribution, #{author}!
 Please add your name and GitHub handle to the file CONTRIBUTORS.md,