diff --git a/entrypoint.sh b/entrypoint.sh
index cd0078f..1337b11 100644
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -24,7 +24,7 @@ sudo service ssh start
   do
     printf "backend_hostname%d = '%s'\n" $n $backend
     printf "backend_port%d = 5432\n" $n
-  n=n + 1
+  ((n+=1))
   done
 } >> /etc/pgpool2/pgpool.conf