diff --git a/doc/Makefile b/doc/Makefile
index fd087f0344..a1f76d7041 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -158,7 +158,7 @@ $(VENV):
 	@( \
 		virtualenv -p $(PYTHON) $(VENV); \
 		. $(VENV)/bin/activate; \
-		pip install Sphinx; \
+		pip install Sphinx==1.5.6; \
 		pip install sphinxcontrib-images; \
 		deactivate;\
 	)