diff --git a/.github/workflows/build-grimp.yml b/.github/workflows/build-grimp.yml
index 0ec3fa06a1f5..4fae1cc0d8e9 100644
--- a/.github/workflows/build-grimp.yml
+++ b/.github/workflows/build-grimp.yml
@@ -61,7 +61,11 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           repository: python-grimp/grimp
-          ref: v${{ env.GRIMP_VERSION }}
+          # Upstream tags a release some time after publishing it to PyPI: 3.18 is on PyPI
+          # (its sdist is identical to the head of upstream's release-v3.18 branch, this
+          # commit) but there is no v3.18 tag yet. Pin that commit for it; drop the entry
+          # once the tag exists.
+          ref: ${{ matrix.version == '3.18' && 'c019ec78ecad8990989464cf7eab8ec23d4775ab' || format('v{0}', matrix.version) }}
           persist-credentials: false
 
       - name: Build wheels
diff --git a/docs/packages/grimp.yaml b/docs/packages/grimp.yaml
index 002a38de5b1c..8016d1908deb 100644
--- a/docs/packages/grimp.yaml
+++ b/docs/packages/grimp.yaml
@@ -47,3 +47,4 @@ versions:
   - filename: grimp-3.17-cp314-cp314t-manylinux_2_34_riscv64.manylinux_2_39_riscv64.whl
     sha256: adf6ad7eb3ad6c83b69a7d6574d5f19956f48073641cf52e57f5af012929069e
     requires-python: '>=3.10'
+- version: '3.18'