diff --git a/mrbgems/mruby-bin-mirb/bintest/mirb.rb b/mrbgems/mruby-bin-mirb/bintest/mirb.rb
index 0515cb136..0058896f1 100644
--- a/mrbgems/mruby-bin-mirb/bintest/mirb.rb
+++ b/mrbgems/mruby-bin-mirb/bintest/mirb.rb
@@ -12,9 +12,9 @@ assert('regression for #1563') do
 end
 
 assert('mirb -d option') do
-  o, _ = Open3.capture2('bin/mirb', :stdin_data => "p $DEBUG\n")
+  o, _ = Open3.capture2('bin/mirb', :stdin_data => "$DEBUG\n")
   assert_true o.include?('=> false')
-  o, _ = Open3.capture2('bin/mirb -d', :stdin_data => "p $DEBUG\n")
+  o, _ = Open3.capture2('bin/mirb -d', :stdin_data => "$DEBUG\n")
   assert_true o.include?('=> true')
 end