diff --git a/doc/src/Build_extras.txt b/doc/src/Build_extras.txt
index c35418ae5f..9841acd1f6 100644
--- a/doc/src/Build_extras.txt
+++ b/doc/src/Build_extras.txt
@@ -763,6 +763,11 @@ a global PLUMED installation or consider downloading PLUMED during the LAMMPS bu
 
 [CMake build]:
 
+When the "-D PKG_USER-PLUMED" flag is included in the cmake command you must ensure that 
+gsl, blas and lapack are installed in locations that are specified in your environment.  There
+are then two additional commands that control the manner in which PLUMED is obtained and linked
+into LAMMPS.
+
 -D DOWNLOAD_PLUMED=value   # download PLUMED for build, value = no (default) or yes
 -D PLUMED_MODE=value       # Linkage mode for PLUMED, value = static (default), shared, or runtime :pre