1 files changed, 1 insertions, 1 deletions
diff --git a/lib/open-uri.rb b/lib/open-uri.rb
index 54afb4d88b..2a72062574 100644
--- a/lib/open-uri.rb
+++ b/lib/open-uri.rb
@@ -82,7 +82,7 @@ module OpenURI
     end
 
     unless mode == nil ||
-           mode == 'r' || mode == 'rb'
+           mode == 'r' || mode == 'rb' ||
            mode == O_RDONLY
       raise ArgumentError.new("invalid access mode #{mode} (#{uri.class} resource is read only.)")
     end