diff --git a/common/modules/io.jsm b/common/modules/io.jsm
index 0aaa3c9e..a60c4ea5 100644
--- a/common/modules/io.jsm
+++ b/common/modules/io.jsm
@@ -836,7 +836,7 @@ unlet s:cpo_save
 
                 let result = io.system(arg);
                 if (result.returnValue != 0)
-                    result.output += "\nshell returned " + res;
+                    result.output += "\nshell returned " + result.returnValue;
 
                 modules.commandline.command = "!" + arg;
                 modules.commandline.commandOutput(<span highlight="CmdOutput">{result.output}</span>);