1 files changed, 19 insertions, 3 deletions
diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index d8a212a04a..56db0945eb 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -1272,10 +1272,26 @@ class Gem::Specification < Gem::BasicSpecification
     array = begin
       Marshal.load str
     rescue ArgumentError => e
-      raise unless e.message.include?("YAML")
+      #
+      # Some very old marshaled specs included references to `YAML::PrivateType`
+      # and `YAML::Syck::DefaultKey` constants due to bugs in the old emitter
+      # that generated them. Workaround the issue by defining the necessary
+      # constants and retrying.
+      #
+      message = e.message
+      raise unless message.include?("YAML::")
+
+      Object.const_set "YAML", Psych unless Object.const_defined?(:YAML)
+
+      if message.include?("YAML::Syck::")
+        YAML.const_set "Syck", YAML unless YAML.const_defined?(:Syck)
+
+        YAML::Syck.const_set "DefaultKey", Class.new if message.include?("YAML::Syck::DefaultKey")
+      elsif message.include?("YAML::PrivateType")
+        YAML.const_set "PrivateType", Class.new
+      end
 
-      Object.const_set "YAML", Psych
-      Marshal.load str
+      retry
     end
 
     spec = Gem::Specification.new