diff --git a/var/spack/repos/builtin/packages/charm/package.py b/var/spack/repos/builtin/packages/charm/package.py
index c8083359908..6bbbf063277 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"
     )