diff --git a/src/Infrastructure/IO/doc/IO_rest.tex b/src/Infrastructure/IO/doc/IO_rest.tex
index 94c23cb204..8108f95cdd 100644
--- a/src/Infrastructure/IO/doc/IO_rest.tex
+++ b/src/Infrastructure/IO/doc/IO_rest.tex
@@ -2,6 +2,11 @@
 
 \begin{enumerate}
 
+% See https://github.com/esmf-org/esmf/issues/131
+\item {\bf I/O of NetCDF files requires a real MPI library.}
+Currently I/O of NetCDF files (which uses PIO) requires a real MPI
+library: it cannot be done with ESMF\_COMM set to "mpiuni".
+
 \item {\bf Limited data formats supported.}
 Currently a small fraction of the anticipated data formats is implemented by 
 ESMF.  The data I/O uses NetCDF format, and ESMF Info