diff --git a/.ci/build_script.sh b/.ci/build_script.sh
index 9c6e01280..bb5567d36 100755
--- a/.ci/build_script.sh
+++ b/.ci/build_script.sh
@@ -1,17 +1,9 @@
 #!/usr/bin/env bash
 
 CI_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-DOCKER_HOME=/home/ko
 # shellcheck source=/dev/null
 source "${CI_DIR}/common.sh"
 
-if [[ -z "${CCACHE_DIR}" ]]; then
-    CCACHE_DIR="${HOME}/.ccache"
-fi
-
-mkdir -p "${CCACHE_DIR}"
-echo "using cache dir: ${CCACHE_DIR}"
-
 docker-make() {
     local cmdlist=(
         'source /home/ko/.bashrc'
@@ -19,10 +11,19 @@ docker-make() {
         'sudo chown -R ko:ko .'
         "env MAKEFLAGS='${MAKEFLAGS}' make $(printf '%q ' "$@")"
     )
+    if [[ -z "${CCACHE_DIR}" ]]; then
+        CCACHE_DIR="$(ccache --get-config cache_dir)"
+    fi
+    mkdir -p "${CCACHE_DIR}"
+    echo "using host cache dir: ${CCACHE_DIR}"
     sudo chmod -R 777 "${CCACHE_DIR}"
+    DOCKER_HOME=/home/ko
+    DOCKER_CCACHE_DIR="${DOCKER_HOME}/.cache/ccache"
+    echo "using docker cache dir: ${DOCKER_CCACHE_DIR}"
     docker run --rm -t \
-        -v "${CCACHE_DIR}:${DOCKER_HOME}/.ccache" \
-        -v "$(pwd):${DOCKER_HOME}/base" "${DOCKER_IMG}" \
+        -e CCACHE_DIR="${DOCKER_CCACHE_DIR}" \
+        -v "${CCACHE_DIR}:${DOCKER_CCACHE_DIR}" \
+        -v "${PWD}:${DOCKER_HOME}/base" "${DOCKER_IMG}" \
         /bin/bash -c "$(printf '%s && ' "${cmdlist[@]}")true"
 }
 
@@ -31,3 +32,5 @@ if [[ -z "${DOCKER_IMG}" ]]; then
 else
     docker-make TARGET="${TARGET}" VERBOSE=1 "$@"
 fi
+
+# vim: sw=4
diff --git a/.circleci/config.yml b/.circleci/config.yml
index 5f8dc1d5c..3c04edf26 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -7,7 +7,7 @@ parameters:
     # Bump this to reset all caches.
     cache_epoch:
       type: integer
-      default: 3
+      default: 4
 
 # }}}