diff --git a/tool/lib/iseq_loader_checker.rb b/tool/lib/iseq_loader_checker.rb
index 1a1a694834d4ae..e7cfc79521e6d7 100644
--- a/tool/lib/iseq_loader_checker.rb
+++ b/tool/lib/iseq_loader_checker.rb
@@ -38,8 +38,10 @@ def self.compare_dump_and_load i1, dumper, loader
     i2
   end
 
-  CHECK_TO_A      = ENV['RUBY_ISEQ_DUMP_DEBUG'] == 'to_a'
-  CHECK_TO_BINARY = ENV['RUBY_ISEQ_DUMP_DEBUG'] == 'to_binary'
+  opt = ENV['RUBY_ISEQ_DUMP_DEBUG']
+  puts "RUBY_ISEQ_DUMP_DEBUG = #{opt}" if opt
+  CHECK_TO_A      = 'to_a'      == opt
+  CHECK_TO_BINARY = 'to_binary' == opt
 
   def self.translate i1
     # check to_a/load_iseq