diff --git a/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/make.defaults b/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/make.defaults
index b1ca6590a6..0131a5e29a 100644
--- a/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/make.defaults
+++ b/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/make.defaults
@@ -80,13 +80,17 @@ LINGUAS="en"
 PORTAGE_BZIP2_COMMAND="lbzip2"
 PORTAGE_BUNZIP2_COMMAND="lbunzip2"
 
-# 2.5G seems to be roughly enough to cache a full CoreOS build.
-CCACHE_SIZE="2.5G"
+# Compression allows keeping a much more complete cache, otherwise the
+# kernel alone will eat 1.2GB instead of 455MB. Using /var/tmp/ccache
+# instead of ${ROOT}/var/tmp/ccache enables sharing results across
+# setup_board --force and between different boards of the same arch.
+CCACHE_COMPRESS=1
+CCACHE_DIR="/var/tmp/ccache"
 
 # Always build binary packages, remove old build logs, avoid running as root.
 FEATURES="buildpkg clean-logs compressdebug parallel-install splitdebug
           userfetch userpriv usersandbox ipc-sandbox network-sandbox
-          -merge-sync"
+          ccache -merge-sync"
 
 # No need to restrict access to build directories in dev environments.
 PORTAGE_WORKDIR_MODE="0755"
diff --git a/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.accept_keywords b/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.accept_keywords
index 3ec702efc3..e28710d9cb 100644
--- a/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.accept_keywords
+++ b/sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.accept_keywords
@@ -116,3 +116,6 @@ dev-util/checkbashisms
 
 # Avoid cross compile error with amd64 stable (elfutils-0.158).
 =dev-libs/elfutils-0.161 ~amd64
+
+# Avoid locking bugs that bit us in the 3.1.x series.
+=dev-util/ccache-3.2.2