diff --git a/lib/jekyll/srcset/tag.rb b/lib/jekyll/srcset/tag.rb
index 9785965..e15e502 100644
--- a/lib/jekyll/srcset/tag.rb
+++ b/lib/jekyll/srcset/tag.rb
@@ -1,4 +1,4 @@
-require "RMagick"
+require "rmagick"
 require "digest/sha1"
 
 module Jekyll