diff --git a/docs/Makefile b/docs/Makefile
index a8345f1e8..ba2bb7b09 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -11,7 +11,10 @@ BUILDDIR      = _build
 # Internal variables.
 PAPEROPT_a4     = --define latex_paper_size=a4
 PAPEROPT_letter = --define latex_paper_size=letter
-ALLSPHINXOPTS   = --doctree-dir $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
+
+ALLSPHINXOPTS   = --doctree-dir $(BUILDDIR)/doctrees \
+                  $(PAPEROPT_$(PAPER)) \
+                  $(SPHINXOPTS) .
 
 .PHONY: help
 help: