diff --git a/docs/docsite/Makefile b/docs/docsite/Makefile
index 7449d5e978..f534dc9c8b 100644
--- a/docs/docsite/Makefile
+++ b/docs/docsite/Makefile
@@ -1,4 +1,4 @@
-OS ?= $(shell uname -s)
+OS := $(shell uname -s)
 SITELIB = $(shell python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"):
 FORMATTER=../../hacking/module_formatter.py
 DUMPER=../../hacking/dump_playbook_attributes.py