Added \platform annotations.
diff --git a/Doc/lib/libposix.tex b/Doc/lib/libposix.tex
index 4bbe6e6..0918ad0 100644
--- a/Doc/lib/libposix.tex
+++ b/Doc/lib/libposix.tex
@@ -1,7 +1,8 @@
 \section{\module{posix} ---
-         The most common \POSIX{} system calls.}
-\declaremodule{builtin}{posix}
+         The most common \POSIX{} system calls}
 
+\declaremodule{builtin}{posix}
+  \platform{UNIX}
 \modulesynopsis{The most common \POSIX{} system calls (normally used
 via module \module{os}).}