new file mode 100644
--- /dev/null
+++ b/build/sparse-profiles/toolchain-build
@@ -0,0 +1,9 @@
+# Profile needed to build toolchain tasks.
+
+# This is probably a little wider than we need it to be. But it is
+# still relatively small and it keeps this profile simple.
+%include build/sparse-profiles/taskgraph
+
+[include]
+# Needed by build-clang.py.
+path:tools/rewriting/
\ No newline at end of file

--- a/taskcluster/taskgraph/transforms/job/toolchain.py
+++ b/taskcluster/taskgraph/transforms/job/toolchain.py
@@ -101,33 +101,34 @@ def docker_worker_toolchain(config, job,
 
     worker = taskdesc['worker']
     worker['artifacts'] = []
     worker['chain-of-trust'] = True
 
     docker_worker_add_public_artifacts(config, job, taskdesc)
     docker_worker_add_tc_vcs_cache(config, job, taskdesc)
     docker_worker_add_gecko_vcs_env_vars(config, job, taskdesc)
-    support_vcs_checkout(config, job, taskdesc)
+    support_vcs_checkout(config, job, taskdesc, sparse=True)
 
     env = worker['env']
     env.update({
         'MOZ_BUILD_DATE': config.params['moz_build_date'],
         'MOZ_SCM_LEVEL': config.params['level'],
         'TOOLS_DISABLE': 'true',
         'MOZ_AUTOMATION': '1',
     })
 
     if run['tooltool-downloads']:
         internal = run['tooltool-downloads'] == 'internal'
         docker_worker_add_tooltool(config, job, taskdesc, internal=internal)
 
     worker['command'] = [
         '/builds/worker/bin/run-task',
         '--vcs-checkout=/builds/worker/workspace/build/src',
+        '--sparse-profile', 'build/sparse-profiles/toolchain-build',
         '--',
         'bash',
         '-c',
         'cd /builds/worker && '
         './workspace/build/src/taskcluster/scripts/misc/{}'.format(
             run['script'])
     ]