diff --git a/documentation/Makefile b/documentation/Makefile
index e144a50b4..5f84a93e3 100644
--- a/documentation/Makefile
+++ b/documentation/Makefile
@@ -11,7 +11,7 @@ SOURCEDIR      = .
 VALEDOCS       ?= $(SOURCEDIR)
 SPHINXLINTDOCS ?= $(SOURCEDIR)
 IMAGEDIRS      = */svg
-BUILDDIR       = _build
+BUILDDIR       ?= _build
 DESTDIR        = final
 SVG2PNG        = rsvg-convert
 SVG2PDF        = rsvg-convert