diff --git a/gtsam/base/treeTraversal-inst.h b/gtsam/base/treeTraversal-inst.h
index 4c6d74806..5d2f1b49a 100644
--- a/gtsam/base/treeTraversal-inst.h
+++ b/gtsam/base/treeTraversal-inst.h
@@ -28,6 +28,7 @@
 #include <vector>
 #include <string>
 #include <memory>
+#include <cassert>
 
 namespace gtsam {