diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index e67c303c1..cea51c5ed 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -20,6 +20,7 @@ jobs:
         include:
           - { jdkVersion: "1.11.0", jvmName: "temurin:1.11.0", extraOpts: '-J-XX:+UnlockExperimentalVMOptions -J-XX:+UseJVMCICompiler' }
           - { jdkVersion: "1.17.0", jvmName: "temurin:1.17.0", extraOpts: '' }
+          - { jdkVersion: "1.21.0", jvmName: "temurin:1.21", extraOpts: '' }
     steps:
       - name: Checkout
         # https://github.com/actions/checkout/releases
@@ -40,11 +41,11 @@ jobs:
         uses: coursier/cache-action@d1039466d0812d6370649b9afb02bbf5f646bacf
 
       - name: Set up JDK ${{ matrix.jdkVersion }}
-        # https://github.com/coursier/setup-action/releases
-        # v1.3.0
-        uses: coursier/setup-action@70323223454ac2a9eb2de46f389b4d045cbcdea5
+        uses: coursier/setup-action@v1.3.4
         with:
           jvm: ${{ matrix.jvmName }}
+          # FIXME default index not giving us access to JDK 21 (yet)
+          jvm-index: https://raw.githubusercontent.com/coursier/jvm-index/32d659500e6c65efb9eee91718a0fb0e797ad4ee/index.json
 
       - name: Run tests with default Scala and Java ${{ matrix.jdkVersion }}
         run: sbt "test" ${{ matrix.extraOpts }}