diff --git a/libuavcan/include/uavcan/protocol/global_time_sync_master.hpp b/libuavcan/include/uavcan/protocol/global_time_sync_master.hpp
index d968894619..2ce741bbfc 100644
--- a/libuavcan/include/uavcan/protocol/global_time_sync_master.hpp
+++ b/libuavcan/include/uavcan/protocol/global_time_sync_master.hpp
@@ -13,6 +13,7 @@
 namespace uavcan
 {
 /**
+ * Ref. M. Gergeleit, H. Streich - "Implementing a Distributed High-Resolution Real-Time Clock using the CAN-Bus"
  * TODO: Enforce max one master per node
  */
 class GlobalTimeSyncMaster : protected LoopbackFrameListenerBase
diff --git a/libuavcan/include/uavcan/protocol/global_time_sync_slave.hpp b/libuavcan/include/uavcan/protocol/global_time_sync_slave.hpp
index 303fb40b48..3d2615a0b5 100644
--- a/libuavcan/include/uavcan/protocol/global_time_sync_slave.hpp
+++ b/libuavcan/include/uavcan/protocol/global_time_sync_slave.hpp
@@ -10,7 +10,10 @@
 
 namespace uavcan
 {
-
+/**
+ * Ref. M. Gergeleit, H. Streich - "Implementing a Distributed High-Resolution Real-Time Clock using the CAN-Bus"
+ * http://modecs.cs.uni-salzburg.at/results/related_documents/CAN_clock.pdf
+ */
 class GlobalTimeSyncSlave : Noncopyable
 {
     typedef MethodBinder<GlobalTimeSyncSlave*,