diff --git a/src/qmckl_error.org b/src/qmckl_error.org
index 595814f..403e22f 100644
--- a/src/qmckl_error.org
+++ b/src/qmckl_error.org
@@ -181,11 +181,11 @@ void qmckl_string_of_error(qmckl_exit_code error, char string[<<MAX_STRING_LENGT
   # Fortran interface
   #+begin_src f90 :tangle (eval fh) :noexport :noweb yes
   interface
-     type (c_ptr) function qmckl_string_of_error (error, string) bind(C)
+     subroutine qmckl_string_of_error (error, string) bind(C)
        use, intrinsic :: iso_c_binding
-       integer (c_int32_t), intent(in), value        :: error
-       character*(<<MAX_STRING_LENGTH()>>), intent(out) :: string
-     end function qmckl_string_of_error
+       integer (c_int32_t), intent(in), value :: error
+       character, intent(out) :: string(<<MAX_STRING_LENGTH()>>)
+     end subroutine qmckl_string_of_error
   end interface
   #+end_src