diff --git a/src/schedulables_tree_widget.cc b/src/schedulables_tree_widget.cc
index 411fbd8..3fd5484 100644
--- a/src/schedulables_tree_widget.cc
+++ b/src/schedulables_tree_widget.cc
@@ -27,6 +27,7 @@
 #include "backend/resource.hh"
 #include "add_request_dialog.hh"
 
+#include <cassert>
 #include <iostream>
 #include <sstream>