diff --git a/sys/security/mac_portacl/mac_portacl.c b/sys/security/mac_portacl/mac_portacl.c
index aceda6908b1..f54319aca93 100644
--- a/sys/security/mac_portacl/mac_portacl.c
+++ b/sys/security/mac_portacl/mac_portacl.c
@@ -341,10 +341,12 @@ sysctl_rules(SYSCTL_HANDLER_ARGS)
 	int error;
 
 	new_string = NULL;
-	if (req->newptr == NULL) {
+	if (req->newptr != NULL) {
 		new_string = malloc(MAC_RULE_STRING_LEN, M_PORTACL,
 		    M_WAITOK | M_ZERO);
+		mtx_lock(&rule_mtx);
 		strcpy(new_string, rule_string);
+		mtx_unlock(&rule_mtx);
 		string = new_string;
 	} else
 		string = rule_string;