diff --git a/lightningd/pay.c b/lightningd/pay.c
index 38e325fe5264..dc3c9a6c7be4 100644
--- a/lightningd/pay.c
+++ b/lightningd/pay.c
@@ -83,8 +83,15 @@ void json_add_payment_fields(struct json_stream *response,
 	if (t->destination != NULL)
 		json_add_node_id(response, "destination", t->destination);
 
-	json_add_amount_msat_compat(response, t->msatoshi,
-				    "msatoshi", "amount_msat");
+	/* If we have a 0 amount delivered at the remote end we simply don't
+	 * know since the onion was generated externally. */
+	if (amount_msat_greater(t->msatoshi, AMOUNT_MSAT(0)))
+		json_add_amount_msat_compat(response, t->msatoshi, "msatoshi",
+					    "amount_msat");
+	else
+		json_add_null(response, "amount_msat");
+
+
 	json_add_amount_msat_compat(response, t->msatoshi_sent,
 				    "msatoshi_sent", "amount_sent_msat");
 	json_add_u64(response, "created_at", t->timestamp);