diff --git a/ChangeLog b/ChangeLog
index 069c17e..441e5f2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-12-05  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* src/openpgp.c (cmd_external_authenticate): Support
+	ACK button for firmware update.
+
 2018-12-04  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* src/openpgp-do.c (gpg_data_copy): Fix for NR_DO_UIF_SIG.
diff --git a/src/openpgp.c b/src/openpgp.c
index 984e715..38cd76b 100644
--- a/src/openpgp.c
+++ b/src/openpgp.c
@@ -1388,6 +1388,13 @@ cmd_external_authenticate (struct eventflag *ccid_comm)
       return;
     }
 
+#ifdef ACKBTN_SUPPORT
+  if (gpg_do_get_uif (GPG_KEY_FOR_SIGNING)
+      || gpg_do_get_uif (GPG_KEY_FOR_DECRYPTION)
+      || gpg_do_get_uif (GPG_KEY_FOR_AUTHENTICATION))
+    eventflag_signal (ccid_comm, EV_EXEC_ACK_REQUIRED);
+#endif
+
   r = rsa_verify (pubkey, FIRMWARE_UPDATE_KEY_CONTENT_LEN,
 		  challenge, signature);
   random_bytes_free (challenge);