diff --git a/Makefile b/Makefile
index 163d3b16f..0fe77e24d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,8 @@
-GITRECEIVE_URL = https://raw.github.com/progrium/gitreceive/master/gitreceive
-SSHCOMMAND_URL = https://raw.github.com/progrium/sshcommand/master/sshcommand
-PLUGINHOOK_URL = https://s3.amazonaws.com/progrium-pluginhook/pluginhook_0.1.0_amd64.deb
-DOCKER_URL = https://launchpad.net/~dotcloud/+archive/lxc-docker/+files/lxc-docker_0.4.2-1_amd64.deb
-STACK_URL = https://s3.amazonaws.com/progrium-dokku/progrium_buildstep.tgz
+GITRECEIVE_URL ?= https://raw.github.com/progrium/gitreceive/master/gitreceive
+SSHCOMMAND_URL ?= https://raw.github.com/progrium/sshcommand/master/sshcommand
+PLUGINHOOK_URL ?= https://s3.amazonaws.com/progrium-pluginhook/pluginhook_0.1.0_amd64.deb
+DOCKER_URL ?= https://launchpad.net/~dotcloud/+archive/lxc-docker/+files/lxc-docker_0.4.2-1_amd64.deb
+STACK_URL ?= https://s3.amazonaws.com/progrium-dokku/progrium_buildstep.tgz
 
 all: dependencies stack install plugins