diff --git a/diag_manager/diag_manager.F90 b/diag_manager/diag_manager.F90
index ab94fe690..be448fcfb 100644
--- a/diag_manager/diag_manager.F90
+++ b/diag_manager/diag_manager.F90
@@ -246,6 +246,7 @@ MODULE diag_manager_mod
   USE fms_diag_outfield_mod, ONLY: fmsDiagOutfieldIndex_type, fmsDiagOutfield_type
   USE fms_diag_fieldbuff_update_mod, ONLY: fieldbuff_update, fieldbuff_copy_missvals, &
    & fieldbuff_copy_fieldvals
+  USE fms_string_utils_mod, ONLY: string
 
   USE netcdf, ONLY: NF90_INT, NF90_FLOAT, NF90_CHAR
 
@@ -4224,7 +4225,7 @@ SUBROUTINE diag_manager_init(diag_model_subset, time_init, err_msg)
 
     ! open diag field log file
     IF ( do_diag_field_log.AND.mpp_pe().EQ.mpp_root_pe() ) THEN
-      open(newunit=diag_log_unit, file='diag_field_log.out', action='WRITE')
+      open(newunit=diag_log_unit, file='diag_field_log.out.'//string(mpp_pe()), action='WRITE')
       WRITE (diag_log_unit,'(777a)') &
            & 'Module',         FIELD_LOG_SEPARATOR, 'Field',     FIELD_LOG_SEPARATOR, &
            & 'Long Name',      FIELD_LOG_SEPARATOR, 'Units',     FIELD_LOG_SEPARATOR, &