diff --git a/Source/utils/handle_ptr.h b/Source/utils/handle_ptr.h
index cb838a517..3f664a970 100644
--- a/Source/utils/handle_ptr.h
+++ b/Source/utils/handle_ptr.h
@@ -13,3 +13,5 @@ struct CloseHandleT {
 
 /// HANDLE is void*, so unique_ptr<void, CloseHandleT> is a RAII HANDLE.
 using HandlePtr = std::unique_ptr<void, CloseHandleT>;
+// https://learn.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-createeventa
+// >If the function fails, the return value is NULL.