diff --git a/doc/Makefile b/doc/Makefile
index fd087f0344c32c1d5dfe45b516555e482060c7c9..a1f76d70417a1842a0972806938943877ba2668a 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;\
 	)