diff --git a/Makefile b/Makefile
index 1294220eb84..357402deb68 100644
--- a/Makefile
+++ b/Makefile
@@ -48,10 +48,10 @@ endif
 
 ifeq ($(shell echo $(OS) | egrep -c 'Darwin|FreeBSD|OpenBSD|DragonFly'),1)
 DATE := $(shell date -j -r $(shell git log -n 1 --format="%at") +%Y%m%d%H%M)
-CPUS := $(shell sysctl hw.ncpu|awk '{print $$2}')
+CPUS ?= $(shell sysctl hw.ncpu|awk '{print $$2}')
 else
 DATE := $(shell date --utc --date="$(GIT_DATE)" +%Y%m%d%H%M)
-CPUS := $(shell nproc)
+CPUS ?= $(shell nproc)
 endif
 
 # DEB build parameters
diff --git a/docs/docsite/Makefile b/docs/docsite/Makefile
index 970c148f4c2..7449d5e9785 100644
--- a/docs/docsite/Makefile
+++ b/docs/docsite/Makefile
@@ -1,11 +1,11 @@
-OS = $(shell uname -s)
+OS ?= $(shell uname -s)
 SITELIB = $(shell python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"):
 FORMATTER=../../hacking/module_formatter.py
 DUMPER=../../hacking/dump_playbook_attributes.py
 ifeq ($(shell echo $(OS) | egrep -ic 'Darwin|FreeBSD|OpenBSD|DragonFly'),1)
-CPUS := $(shell sysctl hw.ncpu|awk '{print $$2}')
+CPUS ?= $(shell sysctl hw.ncpu|awk '{print $$2}')
 else
-CPUS := $(shell nproc)
+CPUS ?= $(shell nproc)
 endif
 
 all: docs