diff --git a/doc/Makefile.in b/doc/Makefile.in
index 2efaa80cf..52b55206d 100644
--- a/doc/Makefile.in
+++ b/doc/Makefile.in
@@ -15,7 +15,7 @@ endif
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
-ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
+ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) $(srcdir)
 # the i18n builder cannot share the environment and doctrees with the others
 I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .