diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 4678f53..a3586e7 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1654,6 +1654,7 @@
 {
     /* Identity len will be encoded on two bytes */
     if( psk_identity               == NULL ||
+        psk_identity_len           == 0    ||
         ( psk_identity_len >> 16 ) != 0    ||
         psk_identity_len > MBEDTLS_SSL_OUT_CONTENT_LEN )
     {