Environment Information

• JRuby version (jruby -v): 9.2.19.0
• Operating system: Ubuntu 20.04.2, macOS 11.4

Expected Behavior

The following code executes without error in Ruby 2.5.8 (and 3.0.2):

module Prepended
  def self.prepended(*) ; end
end

module TestModule
  prepend Prepended

  private_method_defined?(:foo)
  def foo ; end
  private :foo
end

Actual Behavior

In JRuby 9.2.19.0, we get:

NameError: undefined method `foo' for module `TestModule'
              private at org/jruby/RubyModule.java:3139

Let me know if there's a better way to report this bug.