diff --git a/.circleci/config.yml b/.circleci/config.yml
index 13e20bb2b..503375ee0 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -47,12 +47,13 @@ jobs:
 
       - restore_cache:
           keys:
-          - v1-emsdk-{{ checksum "emsdk/Makefile" }}-v6
+          - v1-emsdk-{{ checksum "emsdk/Makefile" }}-v6-
 
       - run:
           name: build
           no_output_timeout: 1200
           command: |
+            ccache -z
             make
             ccache -s
 
@@ -60,7 +61,7 @@ jobs:
           paths:
             - ./emsdk/emsdk
             - ~/.ccache
-          key: v1-emsdk-{{ checksum "emsdk/Makefile" }}-v6
+          key: v1-emsdk-{{ checksum "emsdk/Makefile" }}-v6-{{ .BuildNum }}
 
       - run:
           name: test