diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index f2fca12..705a632 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3241,7 +3241,8 @@
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     mbedtls_pk_context *own_key = mbedtls_ssl_own_key( ssl );
 
-    /* We want to call mbedtls_pk_ec(), which only works on those types. */
+    /* Check if the key is a transparent ECDH key.
+     * This also ensures that it is safe to call mbedtls_pk_ec(). */
     if( mbedtls_pk_get_type( own_key ) != MBEDTLS_PK_ECKEY &&
         mbedtls_pk_get_type( own_key ) != MBEDTLS_PK_ECKEY_DH )
     {