diff --git a/exe/rdbg b/exe/rdbg
index af8280633..1cddfd1f2 100755
--- a/exe/rdbg
+++ b/exe/rdbg
@@ -3,7 +3,9 @@
 require_relative '../lib/debug/config'
 config = DEBUGGER__::Config::parse_argv(ARGV)
 
-case config[:mode]
+# mode is not an actual configuration option
+# it's only used to carry the result of parse_argv here
+case config.delete(:mode)
 when :start
   require 'rbconfig'
 
@@ -18,7 +20,7 @@ when :start
 
 when :attach
   require_relative "../lib/debug/client"
-  ::DEBUGGER__::CONFIG.update config
+  ::DEBUGGER__::CONFIG.set_config **config
 
   begin
     if ARGV.empty? && config[:port]