diff --git a/src/zone_nr.c b/src/zone_nr.c
index c7e2a33..805bd4e 100644
--- a/src/zone_nr.c
+++ b/src/zone_nr.c
@@ -20,11 +20,14 @@
  *   get zone number
  *
  *--------------------------------------------------------------*/
-
+#include "string.h"
 
 int zone_nr(char *comment) {
     int z = 0;
 
+    if (strlen(comment) < 2)
+	return z;
+
     if (comment[0] <= 57 && comment[0] >= 48)
 	z = (comment[0] - 48) * 10;
     if (comment[1] <= 57 && comment[1] >= 48)