diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index ab2ae6f..cce834e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -9261,6 +9261,11 @@
             return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }
 
+#if defined(MBEDTLS_SSL_CID)
+    if( transform->out_cid_len != 0 )
+        transform_expansion += MBEDTLS_SSL_MAX_CID_EXPANSION;
+#endif /* MBEDTLS_SSL_CID */
+
     return( (int)( out_hdr_len + transform_expansion ) );
 }