diff --git a/types/types_setup.F90 b/types/types_setup.F90
index 05cc2c27e7722241a56b9cdc80334b93ac42d95c..a80ca81a0feca052c5dab93f315303ede637ca61 100644
--- a/types/types_setup.F90
+++ b/types/types_setup.F90
@@ -667,7 +667,7 @@ MODULE m_types_setup
 
    END TYPE t_wann
 CONTAINS
-   function calc_nsp_atom(self) result(nsp) 
+   pure function calc_nsp_atom(self) result(nsp) 
       implicit none
       CLASS(t_atoms),INTENT(IN)      :: self
       INTEGER                        :: nsp