diff --git a/oh-my-zsh.sh b/oh-my-zsh.sh
index 3ea88e924..2a206798d 100644
--- a/oh-my-zsh.sh
+++ b/oh-my-zsh.sh
@@ -31,7 +31,7 @@ if [ "$ZSH_THEME" = "random" ]
 then
   themes=($ZSH/themes/*zsh-theme)
   N=${#themes[@]}
-  ((N=RANDOM%N))
+  ((N=(RANDOM%N)+1))
   RANDOM_THEME=${themes[$N]}
   source "$RANDOM_THEME"
   echo "[oh-my-zsh] Random theme '$RANDOM_THEME' loaded..."