diff --git a/Makefile b/Makefile
index d5f376abb5..323731ee7b 100644
--- a/Makefile
+++ b/Makefile
@@ -67,4 +67,4 @@ publish:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile doxy
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) -W $(O)