diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 88b39b724f..dc6647d78a 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4641,6 +4641,11 @@ static int ssl_prepare_record_content( mbedtls_ssl_context *ssl )
             return( ret );
         }
 
+        if( ssl->in_iv + rec.data_offset != ssl->in_msg )
+        {
+            /* Should never happen */
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
 
         ssl->in_msglen = rec.data_len;
         ssl->in_len[0] = (unsigned char)( rec.data_len >> 8 );