diff --git a/engine_details/engine_api/custom_modules_in_cpp.rst b/engine_details/engine_api/custom_modules_in_cpp.rst
index 785d5046a..9c6629b52 100644
--- a/engine_details/engine_api/custom_modules_in_cpp.rst
+++ b/engine_details/engine_api/custom_modules_in_cpp.rst
@@ -86,6 +86,8 @@ And then the cpp file.
 
     #include "summator.h"
 
+    #include "core/object/class_db.h"
+
     void Summator::add(int p_value) {
         count += p_value;
     }