diff --git a/var/spack/repos/builtin/packages/charm/package.py b/var/spack/repos/builtin/packages/charm/package.py
index c80833599083186234d9252da4afe2d9781bc692..6bbbf0632775832a732c630492a34216f2a9c3a1 100644
--- a/var/spack/repos/builtin/packages/charm/package.py
+++ b/var/spack/repos/builtin/packages/charm/package.py
@@ -63,6 +63,7 @@ class Charm(Package):
     variant(
         "build-target",
         default="LIBS",
+        # AMPI also builds charm++, LIBS also builds AMPI and charm++
         values=("charm++", "AMPI", "LIBS"),
         description="Specify the target to build"
     )