diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index e7511ad3a..0781b830a 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -74,6 +74,17 @@ jobs:
           # this context and causes pak's solver to abort.
           sed -i 's/testthat (.*/testthat,/' "$tdir/DESCRIPTION"
           echo "NMREC_PKG=local::$tdir" >>$GITHUB_ENV
+      - name: Check out stringfish
+        if: matrix.config.label == 'oldest'
+        shell: bash
+        run: |
+          # stringfish wasn't added to MPN until 2020-06-25 (after
+          # oldest), and the minimum required version wasn't available
+          # until 2020-07-19.
+          tdir=$(mktemp -d)
+          git clone https://github.com/traversc/stringfish "$tdir"
+          git checkout 86c11e6ebb5cf70f1d74e4abfd0369f08499733a
+          echo "STRINGFISH_PKG=local::$tdir" >>$GITHUB_ENV
       - uses: r-lib/actions/setup-r-dependencies@v2
         with:
           extra-packages: |
@@ -81,6 +92,7 @@ jobs:
             any::rcmdcheck
             ${{ env.MRGMISC_PKG }}
             ${{ env.NMREC_PKG }}
+            ${{ env.STRINGFISH_PKG }}
           upgrade: ${{ matrix.config.label == 'oldest' && 'FALSE' || 'TRUE' }}
       - uses: r-lib/actions/check-r-package@v2
       - name: Check pkgdown