diff --git a/Gemfile b/Gemfile
index 8435662441..0675e346d0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -12,3 +12,6 @@ group :development do
   gem 'gettext'
   gem 'prism', '>= 0.30.0'
 end
+
+# Workaround for https://github.com/mkristian/jar-dependencies/issues/86
+gem "jar-dependencies", "~> 0.4.0", platform: :jruby
diff --git a/test/rdoc/test_rdoc_generator_json_index.rb b/test/rdoc/test_rdoc_generator_json_index.rb
index 62d1ccec95..71b5cd969a 100644
--- a/test/rdoc/test_rdoc_generator_json_index.rb
+++ b/test/rdoc/test_rdoc_generator_json_index.rb
@@ -237,6 +237,16 @@ def test_generate_gzipped
   end
 
   def test_generate_utf_8
+    # JRuby fails this test with:
+    #   Encoding::UndefinedConversionError: "\xC2" from ASCII-8BIT to UTF-8
+    #     org/jruby/RubyIO.java:1639:in `write'
+    #     org/jruby/RubyIO.java:1612:in `write'
+    #     json/ext/GeneratorState.java:232:in `_generate'
+    #     json/ext/GeneratorState.java:137:in `generate'
+    #     /Users/runner/work/rdoc/rdoc/vendor/bundle/jruby/3.1.0/gems/json-2.9.0-java/lib/json/common.rb:824:in `dump'
+    #     /Users/runner/work/rdoc/rdoc/lib/rdoc/generator/json_index.rb:148:in `block in generate'
+    omit if RUBY_PLATFORM =~ /java/
+
     text = "5\xB0"
     text = RDoc::Encoding.change_encoding text, Encoding::ISO_8859_1
     @klass.add_comment comment(text), @top_level