diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f5a3eef2..a7bd4cf2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,7 +47,8 @@ jobs:
         uses: pnpm/action-setup@08c4be7e2e672a47d11bd04269e27e5f3e8529cb # v6.0.0
         with:
           # Keep an explicit pnpm major because this repo's packageManager is Yarn.
-          version: 10
+          # pnpm 10's self-installer requires newer Node runtime features than Node 18 provides.
+          version: ${{ matrix.node == '18.x' && '9' || '10' }}
 
       - name: Setup Yarn (via Corepack)
         if: matrix.pm == 'yarn'
diff --git a/.github/workflows/reusable-test.yml b/.github/workflows/reusable-test.yml
index ca3406fa..69c3cbc7 100644
--- a/.github/workflows/reusable-test.yml
+++ b/.github/workflows/reusable-test.yml
@@ -39,7 +39,8 @@ jobs:
         uses: pnpm/action-setup@08c4be7e2e672a47d11bd04269e27e5f3e8529cb # v6.0.0
         with:
           # Keep an explicit pnpm major because this repo's packageManager is Yarn.
-          version: 10
+          # pnpm 10's self-installer requires newer Node runtime features than Node 18 provides.
+          version: ${{ inputs.node-version == '18.x' && '9' || '10' }}
 
       - name: Setup Yarn (via Corepack)
         if: inputs.package-manager == 'yarn'