"\platform{UNIX}" should really be spelled "\platform{Unix}".
diff --git a/Doc/lib/libgrp.tex b/Doc/lib/libgrp.tex
index 5095806..10f12e8 100644
--- a/Doc/lib/libgrp.tex
+++ b/Doc/lib/libgrp.tex
@@ -2,7 +2,7 @@
          The group database}
 
 \declaremodule{builtin}{grp}
-  \platform{UNIX}
+  \platform{Unix}
 \modulesynopsis{The group database (\function{getgrnam()} and friends).}