diff --git a/libuavcan/include/uavcan/server.hpp b/libuavcan/include/uavcan/server.hpp
index cf7ad585c6..ac8955a280 100644
--- a/libuavcan/include/uavcan/server.hpp
+++ b/libuavcan/include/uavcan/server.hpp
@@ -67,7 +67,7 @@ public:
         StaticAssert<DataTypeKind(DataType::DataTypeKind) == DataTypeKindService>::check();
     }
 
-    int start(Callback callback)
+    int start(const Callback& callback)
     {
         stop();
 
diff --git a/libuavcan/include/uavcan/subscriber.hpp b/libuavcan/include/uavcan/subscriber.hpp
index 7ff0fd0950..1310066edc 100644
--- a/libuavcan/include/uavcan/subscriber.hpp
+++ b/libuavcan/include/uavcan/subscriber.hpp
@@ -43,7 +43,7 @@ public:
         StaticAssert<DataTypeKind(DataType::DataTypeKind) == DataTypeKindMessage>::check();
     }
 
-    int start(Callback callback)
+    int start(const Callback& callback)
     {
         stop();