diff --git a/libs/ardour/ardour/chan_count.h b/libs/ardour/ardour/chan_count.h
index 9f9fd07543..b613f67a3c 100644
--- a/libs/ardour/ardour/chan_count.h
+++ b/libs/ardour/ardour/chan_count.h
@@ -154,7 +154,7 @@ private:
 
 } // namespace ARDOUR
 
-std::ostream& operator<<(std::ostream& o, const ARDOUR::ChanCount& c);
+LIBARDOUR_API std::ostream& operator<<(std::ostream& o, const ARDOUR::ChanCount& c);
 
 #endif // __ardour_chan_count_h__