--- a/docs/Makefile
+++ b/docs/Makefile
@@ -37,7 +37,7 @@ clean:
 	-rm -rf $(BUILDDIR)/*
 
 install-sphinx:
-	$(PYTHON) -m pip install -e ..[docs]
+	: $(PYTHON) -m pip install -e ..[docs]
 
 .PHONY: html
 html: