diff --git a/src/qt/paymentrequest.proto b/src/qt/paymentrequest.proto
index b2281c4c7..d2721a34b 100644
--- a/src/qt/paymentrequest.proto
+++ b/src/qt/paymentrequest.proto
@@ -6,6 +6,8 @@
 // https://en.bitcoin.it/wiki/Payment_Request
 //
 
+syntax = "proto2";
+
 package payments;
 option java_package = "org.bitcoin.protocols.payments";
 option java_outer_classname = "Protos";