diff --git a/src/lib/dbus/Watch.cxx b/src/lib/dbus/Watch.cxx
index a399836a7..c3a0758ee 100644
--- a/src/lib/dbus/Watch.cxx
+++ b/src/lib/dbus/Watch.cxx
@@ -32,6 +32,8 @@
 
 #include "Watch.hxx"
 
+#include <cassert>
+
 namespace ODBus {
 
 WatchManager::Watch::Watch(EventLoop &event_loop,