Hi, Page 429, Line 41-42 specifies for MPI_Fetch_and_op: The datatype argument must be a predefi?ned datatype. I think it should be: The datatype argument must be a MPI basic datatype (cf. Section 5.9.2 on page 176). Reasons: (*) This would be consistent to the reduce functions and MPI_Compare_and_swap and would allow handles returned by MPI_TYPE_CREATE_F90_INTEGER, MPI_TYPE_CREATE_F90_REAL, or MPI_TYPE_F90_COMPLEX. (*) MPI_Compare_and_swap accepts handles created by MPI_TYPE_CREATE_F90_INTEGER ( they are contained in Fortran integer category). (*) Predefined datatypes such as MPI_WCHAR or MPI_PACKED are useless in MPI_Fetch_and_op. Additionally, on Page 430, Line 39: predefined datatypes should be replaced by basic datatypes since Section 5.9.2 defines the MPI basic datatypes and not the predefined datatypes (which are defined in Tables 3.x). Hubert