diff --git a/lib/csv.rb b/lib/csv.rb
index b1f1b80..e294e4f 100644
--- a/lib/csv.rb
+++ b/lib/csv.rb
@@ -1025,8 +1025,7 @@ class << self
     #   CSV.instance(s0) {|csv| :foo } # => :foo
     def instance(data = $stdout, **options)
       # create a _signature_ for this method call, data object and options
-      sig = [data.object_id] +
-            options.values_at(*DEFAULT_OPTIONS.keys)
+      sig = [self, data.object_id, options]
 
       # fetch or create the instance for this signature
       @@instances ||= Hash.new