ruby/rubygems · error · Gem::SafeMarshal::Visitors::ToRuby::UnsupportedError

Unsupported user-defined class #{klass} in marshal stream @

Error message

Unsupported user-defined class #{klass} in marshal stream @ #{stack.join(".")}

What it means

Error "Unsupported user-defined class #{klass} in marshal stream @ #{stack.join(".")}" thrown in ruby/rubygems.

Source

Thrown at lib/rubygems/safe_marshal/visitors/to_ruby.rb:192

      def visit_Gem_SafeMarshal_Elements_Object(o)
        register_object(resolve_class(o.name).allocate)
      end

      def visit_Gem_SafeMarshal_Elements_ObjectLink(o)
        @objects.fetch(o.offset)
      end

      def visit_Gem_SafeMarshal_Elements_SymbolLink(o)
        @symbols.fetch(o.offset)
      end

      SAFE_USER_DEFINED_CLASSES = [::Time, ::Gem::Specification].freeze
      private_constant :SAFE_USER_DEFINED_CLASSES

      def visit_Gem_SafeMarshal_Elements_UserDefined(o)
        klass = resolve_class(o.name)
        unless SAFE_USER_DEFINED_CLASSES.include?(klass)
          raise UnsupportedError.new("Unsupported user-defined class #{klass} in marshal stream", stack: formatted_stack)
        end
        register_object(call_method(klass, :_load, o.binary_string))
      end

      def visit_Gem_SafeMarshal_Elements_UserMarshal(o)
        klass = resolve_class(o.name)
        compat = COMPAT_CLASSES.fetch(klass, nil)
        idx = @objects.size
        object = register_object(call_method(compat || klass, :allocate))

        push_stack :data
        ret = call_method(object, :marshal_load, visit(o.data))

        if compat
          object = @objects[idx] = ret
        end

        object

View on GitHub (pinned to 86cbb817a3)

Solutions

1. The metadata embeds an unsupported user-defined class; rebuild the gem with a current RubyGems

When it happens

Trigger: Thrown at lib/rubygems/safe_marshal/visitors/to_ruby.rb:192 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of ruby/rubygems@86cbb817a3 (2026-08-23). Data as JSON: /api/errors/7095027f41d276e5. Report an issue: GitHub.