diff --git a/doc/Makefile b/doc/Makefile
index d1bd5fdaf7..895a4aa90d 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -194,7 +194,7 @@ $(VENV):
 		$(VIRTUALENV) -p $(PYTHON) $(VENV); \
 		. $(VENV)/bin/activate; \
 		pip install --upgrade pip; \
-               pip install Sphinx=2.4.4; \
+		pip install Sphinx==2.4.4; \
 		pip install sphinxcontrib-spelling ;\
 		pip install breathe; \
 		deactivate;\