diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 69a46b9..e450207 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -9171,8 +9171,13 @@
     ssl_conf_remove_psk( conf );
 
     /* Check and set raw PSK */
-    if( psk == NULL || psk_len > MBEDTLS_PSK_MAX_LEN )
+    if( psk == NULL )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    if( psk_len == 0 )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    if( psk_len > MBEDTLS_PSK_MAX_LEN )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
     if( ( conf->psk = mbedtls_calloc( 1, psk_len ) ) == NULL )
         return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
     conf->psk_len = psk_len;