diff --git a/docs/Makefile b/docs/Makefile
index 1518a91bb..9ba3af64c 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    ?=
 SPHINXBUILD   ?= sphinx-build
+BUILDDIR      ?= _build
 SOURCEDIR     = .
-BUILDDIR      = _build
 
 # Put it first so that "make" without argument is like "make help".
 help:
diff --git a/docs/make.bat b/docs/make.bat
index 2119f5109..24c26b229 100644
--- a/docs/make.bat
+++ b/docs/make.bat
@@ -7,8 +7,10 @@ REM Command file for Sphinx documentation
 if "%SPHINXBUILD%" == "" (
 	set SPHINXBUILD=sphinx-build
 )
+if "%BUILDDIR%" == "" (
+	set BUILDDIR=_build
+)
 set SOURCEDIR=.
-set BUILDDIR=_build
 
 if "%1" == "" goto help