diff --git a/Makefile b/Makefile
index 997cfaa..b348fac 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,12 @@
-init:
+.PHONY: all
+all: test
+
+.PHONY: init
+init: .pip_install_timestamp
+.pip_install_timestamp: requirements.txt
 	pip install -r requirements.txt
+	touch .pip_install_timestamp
 
-test:
+.PHONY: test
+test: .pip_install_timestamp
 	nosetests tests