diff --git a/runas.sh b/runas.sh
index 8e9b6a4..1b14e13 100755
--- a/runas.sh
+++ b/runas.sh
@@ -26,7 +26,7 @@ function process_args {
     exit 1
   fi
 
-  if [[ ! "$UMASK" =~ ^[0-7][0-7][0-7][0-7]$ ]]
+  if [[ ! "$UMASK" =~ ^0[0-7][0-7][0-7]$ ]]
   then
     echo "The umask value $UMASK is not valid. It must be an octal number such as 0022"
     exit 1