diff --git a/site_utils/bind_mysql_to_cpuset.sh b/site_utils/bind_mysql_to_cpuset.sh
index 60d5d66..c7975d5 100755
--- a/site_utils/bind_mysql_to_cpuset.sh
+++ b/site_utils/bind_mysql_to_cpuset.sh
@@ -80,7 +80,7 @@
 function get_mysql_pid() {
   local pid=""
 
-  if [ $# -gt 0 ]; then
+  if [ $# -gt 0 ] && [ ! -z "$1" ]; then
     # Use user-provided PID.
     pid=$1
   elif [ ! -z ${MYSQL_PID_PATH} -a -f ${MYSQL_PID_PATH} ]; then