diff --git a/lib/jekyll/site.rb b/lib/jekyll/site.rb
index a095c81f..43618dc2 100644
--- a/lib/jekyll/site.rb
+++ b/lib/jekyll/site.rb
@@ -419,7 +419,7 @@ module Jekyll
     end
 
     def has_yaml_header?(file)
-      !!(File.open(file, "rb").read =~ /\A---\r?\n/)
+      !!(File.open(file, "rb").read(5) =~ /\A---\r?\n/)
     end
 
     def limit_posts!