diff --git a/Makefile b/Makefile
index 7fc1944cd..8b4df67be 100644
--- a/Makefile
+++ b/Makefile
@@ -60,10 +60,13 @@ data/data.js: $(DATA_FILES)
 	js/lib/locale.js \
 	locale/*.js
 
-iD.js: Makefile
+iD.js: node_modules Makefile
 	@rm -f $@
 	cat $(filter %.js,$^) > $@
 
+node_modules:
+	npm install
+
 %.min.js: %.js Makefile
 	@rm -f $@
 	$(JS_COMPILER) $< -c -m -o $@