diff --git a/Makefile b/Makefile
index 517d6226..437336e4 100644
--- a/Makefile
+++ b/Makefile
@@ -6,9 +6,10 @@ TCL_FORMAT ?= utils//tcl-reformat.sh
 
 IN_ENV = if [ -e env/bin/activate ]; then . env/bin/activate; fi;
 env:
-	virtualenv --python=python3 env
+	virtualenv --python=python3 --system-site-packages env
 	. env/bin/activate; pip install -r requirements.txt
 	ln -sf $(PWD)/prjxray env/lib/python3.*/site-packages/
+	python -c "import yaml" || (echo "Unable to find python-yaml" && exit 1)
 
 build:
 	git submodule update --init --recursive