diff --git a/Dockerfile.dapper b/Dockerfile.dapper
index 4f89341..35ec61a 100644
--- a/Dockerfile.dapper
+++ b/Dockerfile.dapper
@@ -12,5 +12,9 @@ ENV SHELL /bin/bash
 ENV HOME ${DAPPER_SOURCE}
 WORKDIR ${DAPPER_SOURCE}
 
+ENV KERNEL_TAG=Ubuntu-4.4.0-47.68-rancher1
+ENV KERNEL_URL=https://github.com/rancher/linux/archive/${KERNEL_TAG}.tar.gz
+ENV KERNEL_SHA1=9e93ea7fc7acf9988572c1961a32ddc17e042b50
+
 ENTRYPOINT ["./scripts/entry"]
 CMD ["ci"]
diff --git a/scripts/build-common b/scripts/build-common
index 245aa09..74064fe 100644
--- a/scripts/build-common
+++ b/scripts/build-common
@@ -1,8 +1,6 @@
 #!/bin/bash
 set -e
 
-: ${KERNEL_URL:="https://github.com/rancher/linux/archive/Ubuntu-4.4.0-47.68-rancher1.tar.gz"}
-: ${KERNEL_SHA1:="9e93ea7fc7acf9988572c1961a32ddc17e042b50"}
 : ${ARTIFACTS:=$(pwd)/assets}
 : ${BUILD:=/usr/src}
 : ${CONFIG:=$(pwd)/config}