diff --git a/doc/source/user_guide/ug_implementation.rst b/doc/source/user_guide/ug_implementation.rst
index ef60ee857..101a770f8 100644
--- a/doc/source/user_guide/ug_implementation.rst
+++ b/doc/source/user_guide/ug_implementation.rst
@@ -1205,7 +1205,7 @@ in both netCDF and PIO output.
 netCDF requires CICE compilation with a netcdf library built externally.  
 PIO requires CICE compilation with a PIO and netcdf library built externally.  
 Both netCDF and PIO can be built with many options which may require additional libraries
-such as hdf5 or pnetCDF.
+such as MPI, hdf5, or pnetCDF.
 
 .. _history: