default_scope Errors with named_scope

When using default_scope in conjunction with named_scope, a default_scope that has been defined with :condition as a String, rather than a hash will throw a "TypeError: can't convert String into Hash" from

activerecord/lib/active_record/base.rb:2132: in 'merge'
activerecord/lib/active_record/base.rb:2132: in 'with_scope'
activerecord/lib/active_record/base.rb:2110: in 'each'
activerecord/lib/active_record/base.rb:2110: in 'inject'
activerecord/lib/active_record/base.rb:2110: in 'with_scope'

The default scope works find on its own, but calling a named_scope will throw the error when, presumably, trying to merge the scopes.

default_scope {:conditions => ["expires_at > ?", Time.now] }
named_scope :globals { :conditions => {:global => true } }