--- a/testing/mozbase/mozdebug/mozdebug/mozdebug.py
+++ b/testing/mozbase/mozdebug/mozdebug/mozdebug.py
@@ -118,17 +118,17 @@ def get_debugger_info(debugger, debugger
         ['path', 'interactive', 'args', 'requiresEscapedArgs']
     )
 
     debugger_arguments = get_debugger_info('args', [])
 
     # Extend the default arguments for the chosen debugger with the ones passed in, if any.
     if debuggerArgs:
         # Append the provided debugger arguments at the end of the arguments list.
-        debugger_arguments.extend(debuggerArgs)
+        debugger_arguments += debuggerArgs.split()
 
     # Override the default debugger interactive mode if needed.
     debugger_interactive = get_debugger_info('interactive', False)
     if debuggerInteractive:
         debugger_interactive = debuggerInteractive
 
     d = DebuggerInfo(
         debuggerPath,