ruby/rubygems · error · Psych::DisallowedClass

Tried to load unspecified class: #{tag}

Error message

Tried to load unspecified class: #{tag}

What it means

Error "Tried to load unspecified class: #{tag}" thrown in ruby/rubygems.

Source

Thrown at lib/rubygems/yaml_serializer.rb:662

      def pairs_to_hash(node)
        result = {}
        node.pairs.each do |key_node, value_node|
          key = key_node.is_a?(Scalar) ? key_node.value.to_s : build_node(key_node).to_s
          result[key] = build_node(value_node)
        end
        result
      end

      def validate_tag!(tag)
        return if @permitted_classes.include?(tag)
        raise_disallowed_class!(tag)
      end

      def raise_disallowed_class!(tag)
        if defined?(Psych::VERSION)
          raise Psych::DisallowedClass.new("load", tag)
        else
          raise Psych::DisallowedClass, "Tried to load unspecified class: #{tag}"
        end
      end

      def validate_symbol!(name)
        return if @permitted_symbols.empty? || @permitted_symbols.include?(name)

        label = ":#{name}"
        if defined?(Psych::VERSION)
          raise Psych::DisallowedClass.new("load", label)
        else
          raise Psych::DisallowedClass, "Tried to load unspecified class: #{label}"
        end
      end

      def normalize_specification_version!(hash)
        val = hash["specification_version"]
        return unless val && !val.is_a?(Integer)
        hash["specification_version"] = val.to_i if val.is_a?(String) && /\A\d+\z/.match?(val)

View on GitHub (pinned to 86cbb817a3)

Solutions

1. Do not trust the YAML: it references a class outside the permitted set; re-download from the official source

When it happens

Trigger: Thrown at lib/rubygems/yaml_serializer.rb:662 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/98d778cd6809fa05. Report an issue: GitHub.