1 files changed, 1 insertions, 1 deletions
diff --git a/lib/open-uri.rb b/lib/open-uri.rb
index 8ff5a10b86..132a1f4662 100644
--- a/lib/open-uri.rb
+++ b/lib/open-uri.rb
@@ -98,7 +98,7 @@ module OpenURI
 
     unless mode == nil ||
            mode == 'r' || mode == 'rb' ||
-           mode == O_RDONLY
+           mode == File::RDONLY
       raise ArgumentError.new("invalid access mode #{mode} (#{uri.class} resource is read only.)")
     end