diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 036876cb0..3802e230e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7742,6 +7742,7 @@ void mbedtls_ssl_config_free( mbedtls_ssl_config *conf )
     {
         mbedtls_zeroize( conf->psk, conf->psk_len );
         mbedtls_free( conf->psk );
+        conf->psk = NULL;
         conf->psk_len = 0;
     }
 
@@ -7749,6 +7750,7 @@ void mbedtls_ssl_config_free( mbedtls_ssl_config *conf )
     {
         mbedtls_zeroize( conf->psk_identity, conf->psk_identity_len );
         mbedtls_free( conf->psk_identity );
+        conf->psk_identity = NULL;
         conf->psk_identity_len = 0;
     }
 #endif