diff --git a/lib/net/imap.rb b/lib/net/imap.rb
index c40400b7..07e5a317 100644
--- a/lib/net/imap.rb
+++ b/lib/net/imap.rb
@@ -3253,6 +3253,10 @@ def search_args(keys, charset_arg = nil, return: nil, charset: nil)
         esearch = false
       in [_, Array[RETURN_WHOLE, _, *] | RETURN_START]
         raise ArgumentError, "conflicting return options"
+      in [_, Array[RETURN_WHOLE, _, *]] # workaround for https://bugs.ruby-lang.org/issues/20956
+        raise ArgumentError, "conflicting return options"
+      in [_, RETURN_START]              # workaround for https://bugs.ruby-lang.org/issues/20956
+        raise ArgumentError, "conflicting return options"
       in [return_opts, keys]
         return_opts = convert_return_opts(return_opts)
         esearch = true