diff --git a/include/cppast/cpp_entity_ref.hpp b/include/cppast/cpp_entity_ref.hpp
index 29afd60..55d5943 100644
--- a/include/cppast/cpp_entity_ref.hpp
+++ b/include/cppast/cpp_entity_ref.hpp
@@ -9,6 +9,7 @@
 
 #include <type_safe/variant.hpp>
 
+#include <cppast/detail/assert.hpp>
 #include <cppast/cpp_entity_index.hpp>
 
 namespace cppast