diff --git a/plugins/mysql/mysql_report b/plugins/mysql/mysql_report
index 798021e8..8ae0e02c 100755
--- a/plugins/mysql/mysql_report
+++ b/plugins/mysql/mysql_report
@@ -92,7 +92,7 @@ graph_vlabel ${vlabel}
 graph_category ${category}
 graph_info ${info}
 EOH1
-  [[ -n "${period}" ]] && echo "graph_period ${period}"
+  [ -n "${period}" ] && echo "graph_period ${period}"
   I=1
   for name in ${names}; do
     eval iquery='${query_'${name}'}'