diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 283e80a..552a099 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3718,6 +3718,9 @@
 {
     int ret;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> send alert message" ) );
 
     ssl->out_msgtype = MBEDTLS_SSL_MSG_ALERT;
@@ -5917,6 +5920,9 @@
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
 #if defined(MBEDTLS_SSL_CLI_C)
     if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
         ret = mbedtls_ssl_handshake_client_step( ssl );
@@ -5936,6 +5942,9 @@
 {
     int ret = 0;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> handshake" ) );
 
     while( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
@@ -6031,6 +6040,9 @@
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
 #if defined(MBEDTLS_SSL_SRV_C)
     /* On server, just send the request */
     if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
@@ -6108,6 +6120,9 @@
     int ret, record_read = 0;
     size_t n;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> read" ) );
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
@@ -6451,6 +6466,9 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write" ) );
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
 #if defined(MBEDTLS_SSL_RENEGOTIATION)
     if( ( ret = ssl_check_ctr_renegotiate( ssl ) ) != 0 )
     {
@@ -6486,6 +6504,9 @@
 {
     int ret;
 
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write close notify" ) );
 
     if( ssl->out_left != 0 )