diff --git a/docs/Makefile b/docs/Makefile
index 21666bb84..5d20fc74c 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -2,11 +2,11 @@
 #
 
 # You can set these variables from the command line, and also
-# from the environment for the first two.
+# from the environment for the first three.
 SPHINXOPTS    ?= -n
 SPHINXBUILD   ?= sphinx-build
+BUILDDIR      ?= _build
 SOURCEDIR     = .
-BUILDDIR      = _build
 
 # Put it first so that "make" without argument is like "make help".
 help: