diff --git a/lib/debug/session.rb b/lib/debug/session.rb
index 3db2f45da..0a3174473 100644
--- a/lib/debug/session.rb
+++ b/lib/debug/session.rb
@@ -82,7 +82,7 @@ def last_line
   def first_line
     self.to_a[4][:code_location][0]
   end unless method_defined?(:first_line)
-end
+end if defined?(RubyVM::InstructionSequence)
 
 module DEBUGGER__
   PresetCommands = Struct.new(:commands, :source, :auto_continue)
@@ -133,7 +133,7 @@ def initialize
       @commands = {}
       @unsafe_context = false
 
-      @has_keep_script_lines = RubyVM.respond_to? :keep_script_lines
+      @has_keep_script_lines = defined?(RubyVM.keep_script_lines)
 
       @tp_load_script = TracePoint.new(:script_compiled){|tp|
         eval_script = tp.eval_script unless @has_keep_script_lines
diff --git a/lib/debug/source_repository.rb b/lib/debug/source_repository.rb
index ddcfd6e93..52e43cf7d 100644
--- a/lib/debug/source_repository.rb
+++ b/lib/debug/source_repository.rb
@@ -22,7 +22,7 @@ def get iseq
       end
     end
 
-    if RubyVM.respond_to? :keep_script_lines
+    if defined?(RubyVM.keep_script_lines)
       # Ruby 3.1 and later
       RubyVM.keep_script_lines = true
       require 'objspace'