diff --git a/.github/workflows/code_size.yml b/.github/workflows/code_size.yml
index 34bdf744cb..f82d1d0c73 100644
--- a/.github/workflows/code_size.yml
+++ b/.github/workflows/code_size.yml
@@ -33,7 +33,7 @@ jobs:
     - name: Build
       run: tools/ci.sh code_size_build
     - name: Compute code size difference
-      run: tools/metrics.py diff ~/size0 ~/size1 | tee diff
+      run: source tools/ci.sh && ci_code_size_report
     - name: Save PR number
       if: github.event_name == 'pull_request'
       env:
diff --git a/tools/ci.sh b/tools/ci.sh
index 64c9d465d8..17044edf28 100755
--- a/tools/ci.sh
+++ b/tools/ci.sh
@@ -122,6 +122,11 @@ function ci_code_size_build {
     return $STATUS
 }
 
+function ci_code_size_report {
+    # Allow errors from tools/metrics.py to propagate out of the pipe above.
+    (set -o pipefail; tools/metrics.py diff ~/size0 ~/size1 | tee diff)
+}
+
 ########################################################################################
 # .mpy file format