diff --git a/tools/python.mk b/tools/python.mk
index 89d2c2ae2..00f46af38 100644
--- a/tools/python.mk
+++ b/tools/python.mk
@@ -26,7 +26,8 @@ $(VENV):
 install: $(VENV)
 	source $(VENV)/bin/activate
 	pip install --upgrade pip setuptools wheel
-	pip install $(SHARED_DEV_REQUIREMENTS) $(PIP_INSTALL)
+	pip install $(SHARED_DEV_REQUIREMENTS)
+	[[ -z "$(PIP_INSTALL)" ]] || pip install $(PIP_INSTALL)
 
 .PHONY: .format
 .format: $(VENV)