diff --git a/Makefile b/Makefile
index b447cc50b..17a0e4cf7 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@ docker/weave:
 	curl -L git.io/weave -o docker/weave
 	chmod u+x docker/weave
 
-$(SCOPE_EXPORT): $(APP_EXE) $(PROBE_EXE) $(DOCKER_DISTRIB) docker/weave $(RUNSVINIT) docker/Dockerfile docker/run-app docker/run-probe docker/entrypoint.sh docker/ca-certificates.crt
+$(SCOPE_EXPORT): backend $(DOCKER_DISTRIB) docker/weave $(RUNSVINIT) docker/Dockerfile docker/run-app docker/run-probe docker/entrypoint.sh docker/ca-certificates.crt
 	@if [ -z '$(DOCKER_SQUASH)' ] ; then echo "Please install docker-squash by running 'make deps' (and make sure GOPATH/bin is in your PATH)." && exit 1 ; fi
 	cp $(APP_EXE) $(PROBE_EXE) docker/
 	cp $(DOCKER_DISTRIB) docker/docker.tgz
@@ -91,13 +91,13 @@ $(SCOPE_BACKEND_BUILD_UPTODATE): backend/*
 	touch $@
 
 backend: $(SCOPE_BACKEND_BUILD_UPTODATE)
-	docker run -ti $(RM) -v $(shell pwd):/go/src/github.com/weaveworks/scope $(SCOPE_BACKEND_BUILD_IMAGE) /build.bash
+	docker run -ti $(RM) -v $(GOPATH)/src:/go/src -e GOARCH -e GOOS $(SCOPE_BACKEND_BUILD_IMAGE) /build.bash
 
 frontend: $(SCOPE_UI_BUILD_UPTODATE)
 
 clean:
 	go clean ./...
-	rm -rf $(SCOPE_EXPORT) $(SCOPE_UI_BUILD_EXPORT) $(APP_EXE) $(PROBE_EXE) client/build/app.js docker/weave
+	rm -rf $(SCOPE_EXPORT) $(SCOPE_UI_BUILD_UPTODATE) $(SCOPE_BACKEND_BUILD_UPTODATE) $(APP_EXE) $(PROBE_EXE) client/build/app.js docker/weave
 
 deps:
 	go get -u -f -tags netgo \
diff --git a/README.md b/README.md
index f470baeb7..48824c14f 100644
--- a/README.md
+++ b/README.md
@@ -142,15 +142,13 @@ sudo scope launch --service-token=<token>
 The build is in five stages. `make deps` installs some tools we use later in
 the build. `make frontend` builds a UI build image with all NPM dependencies.
 `make static` compiles the UI into `static.go` which is part of the repository
-for convenience. `make backend` builds the backend Go app which then includes
-the static files. The final `make` pushes the app into a Docker image called
-**weaveworks/scope**.
+for convenience. The final `make` builds the app and probe, in a container,
+and pushes the lot into a Docker image called **weaveworks/scope**.
 
 ```
 make deps
 make frontend
 make static
-make backend
 make
 ```
 
diff --git a/backend/build.bash b/backend/build.bash
index 134cf557b..e329d22f4 100755
--- a/backend/build.bash
+++ b/backend/build.bash
@@ -1,12 +1,11 @@
 #!/bin/bash
 
-set -x
+set -eux
 
 # Mount the scope repo:
 #  -v $(pwd):/go/src/github.com/weaveworks/scope
 
-cd /go/src/github.com/weaveworks/scope
-make deps
+cd $GOPATH/src/github.com/weaveworks/scope
 make app/scope-app
 make probe/scope-probe
 
diff --git a/circle.yml b/circle.yml
index 61f182437..63fc47c9c 100644
--- a/circle.yml
+++ b/circle.yml
@@ -7,7 +7,7 @@ machine:
   services:
     - docker
   environment:
-    GOPATH: /home/ubuntu:$GOPATH
+    GOPATH: /home/ubuntu
     TOOLS: /home/ubuntu/src/github.com/weaveworks/tools
     SRCDIR: /home/ubuntu/src/github.com/weaveworks/scope
     PATH: $PATH:$HOME/.local/bin
@@ -36,13 +36,17 @@ dependencies:
     - mkdir -p $(dirname $SRCDIR)
     - cp -r $(pwd)/ $SRCDIR
     - cd $SRCDIR/client; $TOOLS/rebuild-image weaveworks/scope-ui-build . Dockerfile package.json webpack.production.config.js .eslintrc
+    - cd $SRCDIR/backend; $TOOLS/rebuild-image weaveworks/scope-backend-build . Dockerfile build.sh
+    - touch $SRCDIR/.scope_backend_build.uptodate
 
 test:
   override:
     - cd $SRCDIR; $TOOLS/lint .
     - cd $SRCDIR; make RM= client-test
     - cd $SRCDIR; make RM= static
-    - cd $SRCDIR; rm -f app/scope-app probe/scope-probe; make
+    - cd $SRCDIR; rm -f app/scope-app probe/scope-probe; GOARCH=arm make RM= backend
+    - cd $SRCDIR; rm -f app/scope-app probe/scope-probe; GOOS=darwin make RM= backend
+    - cd $SRCDIR; rm -f app/scope-app probe/scope-probe; make RM=
     - cd $SRCDIR; $TOOLS/test -slow
     - cd $SRCDIR/experimental; make
     - test -z "$SECRET_PASSWORD" || (cd $SRCDIR/integration; ./gce.sh setup)