Environment Information

• jruby 10.0.4.0-SNAPSHOT (3.4.5) 2026-02-22 ffffffffff OpenJDK 64-Bit Server VM 21.0.10+7 on 21.0.10+7 +indy +jit [x86_64-linux] (master)
• Linux meow4 6.18.4-1-MANJARO #1 SMP PREEMPT_DYNAMIC Thu, 08 Jan 2026 12:46:08 +0000 x86_64 GNU/Linux

Expected Behavior

Given this file:

class A < BasicObject
  define_method(:respond_to?, ::Kernel.instance_method(:respond_to?))
end

puts A.new.respond_to?(:asdf) rescue nil

class B
  undef :respond_to_missing?
end

puts B.new.respond_to?(:asdf)

I expect:

false
false

Actual Behavior

NoMethodError: undefined method 'respond_to_missing?' for an instance of B
  respond_to? at org/jruby/RubyKernel.java:2223
       <main> at ./test.rb:11

(Note the rescue for A, that's why the error only happens for B, otherwise there is no difference.)