diff --git a/.github/actions/setup-deps/action.yml b/.github/actions/setup-deps/action.yml
index 81b94054..2a78282d 100644
--- a/.github/actions/setup-deps/action.yml
+++ b/.github/actions/setup-deps/action.yml
@@ -56,8 +56,11 @@ runs:
           # Push the gcc node now, BEFORE `spack compiler find` registers it as an
           # external -- externals are excluded from `buildcache push`. This is what
           # lets CI pull gcc from the cache (~1 min) instead of building it (~1 h).
+          # --allow-missing: when gcc itself was pulled from the cache, its
+          # build-time dependencies are not installed locally and would
+          # otherwise fail the push.
           spack mirror set --oci-username ${{ github.actor }} --oci-password-variable GITHUB_TOKEN ghcr-buildcache
-          spack buildcache push --unsigned ghcr-buildcache /$gcc_hash
+          spack buildcache push --unsigned --allow-missing ghcr-buildcache /$gcc_hash
         fi
         spack compiler find "$(spack location -i /$gcc_hash)"
         echo "::endgroup::"
diff --git a/.github/workflows/buildcache.yml b/.github/workflows/buildcache.yml
index 955eafd5..ab7179e6 100644
--- a/.github/workflows/buildcache.yml
+++ b/.github/workflows/buildcache.yml
@@ -50,7 +50,10 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           spack -e fairmq mirror set --oci-username ${{ github.actor }} --oci-password-variable GITHUB_TOKEN ghcr-buildcache
-          spack -e fairmq buildcache push --unsigned ghcr-buildcache
+          # --allow-missing: build-time dependencies of specs that were
+          # satisfied from the buildcache are not installed locally and
+          # would otherwise fail the whole push.
+          spack -e fairmq buildcache push --unsigned --allow-missing ghcr-buildcache
 
   update-index:
     if: github.repository == 'FairRootGroup/FairMQ' && !cancelled()