diff --git a/test/ruby/test_jit.rb b/test/ruby/test_jit.rb
index 7627b2c048..7fe58ea336 100644
--- a/test/ruby/test_jit.rb
+++ b/test/ruby/test_jit.rb
@@ -877,10 +877,8 @@ class TestJIT < Test::Unit::TestCase
         Process.waitpid(pid)
       end;
       success_count = err.scan(/^#{JIT_SUCCESS_PREFIX}:/).size
-      assert_equal(3, success_count)
-
-      lines = err.lines
       debug_info = "stdout:\n```\n#{out}\n```\n\nstderr:\n```\n#{err}```\n"
+      assert_equal(3, success_count, debug_info)
 
       # assert no remove error
       assert_equal("Successful MJIT finish\n" * 2, err.gsub(/^#{JIT_SUCCESS_PREFIX}:[^\n]+\n/, ''), debug_info)