diff --git a/admin/horace_mex_mpi.m b/admin/horace_mex_mpi.m
index 8dafd646bf..bf0c4db071 100644
--- a/admin/horace_mex_mpi.m
+++ b/admin/horace_mex_mpi.m
@@ -5,7 +5,7 @@
 % Manually modify this script to specify the mpi libraries location in your
 % system.
 %
-use_her_mpich = false;
+use_her_mpich = true;
 verbose = nargin > 0;
 pths = horace_paths;
 
@@ -70,7 +70,7 @@
 
 build_version_h(pths.root)
 try
-    opt = sprintf('CXXFLAGS=$CFLAGS -fopenmp -std=c++11 -Wl,-rpath=%s,--enable-new-dtags,--no-undefined,-fopenmp',mpi_lib_folder);
+    opt = sprintf('CXXFLAGS=$CFLAGS -fopenmp -std=c++17 -Wl,-rpath=%s,--enable-new-dtags,--no-undefined,-fopenmp',mpi_lib_folder);
     if isempty(opt_file)
         mex('-v',add_include{:},opt,input_files{:},...
             mpi_lib{:},'-outdir',outdir);