diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 096efc3..c503170 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,6 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [ 'ubuntu-latest', 'windows-latest', 'macos-latest' ]
+        jvm: [ 11, 17, 21 ]
 
     runs-on: ${{ matrix.os }}
 
@@ -23,7 +24,7 @@ jobs:
 
       - uses: actions/setup-java@v3
         with:
-          java-version: 11
+          java-version: ${{ matrix.jvm }}
           distribution: adopt
 
       - run: mvn --batch-mode verify
diff --git a/.github/workflows/checkstyle.yml b/.github/workflows/checkstyle.yml
index 4c15f9c..875e7ab 100644
--- a/.github/workflows/checkstyle.yml
+++ b/.github/workflows/checkstyle.yml
@@ -19,7 +19,7 @@ jobs:
 
       - uses: actions/setup-java@v3
         with:
-          java-version: 11
+          java-version: 17
           distribution: adopt
 
       - name: Generate demo report
diff --git a/.github/workflows/codecov.yml b/.github/workflows/codecov.yml
index 8649d11..082de57 100644
--- a/.github/workflows/codecov.yml
+++ b/.github/workflows/codecov.yml
@@ -19,7 +19,7 @@ jobs:
 
       - uses: actions/setup-java@v3
         with:
-          java-version: 11
+          java-version: 17
           distribution: adopt
 
       - name: Generate code coverage
diff --git a/.github/workflows/sonarcloud.yml b/.github/workflows/sonarcloud.yml
index 1a8fa60..f8d5ffc 100644
--- a/.github/workflows/sonarcloud.yml
+++ b/.github/workflows/sonarcloud.yml
@@ -17,7 +17,7 @@ jobs:
 
       - uses: actions/setup-java@v3
         with:
-          java-version: 11
+          java-version: 17
           distribution: adopt
 
       - name: Build with Maven
diff --git a/pom.xml b/pom.xml
index 912490b..aac5f62 100644
--- a/pom.xml
+++ b/pom.xml
@@ -170,6 +170,10 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>3.2.2</version>
                 <configuration>
+                    <!-- Allow JUnit to access the test classes -->
+                    <argLine>
+                        --add-opens java.base/java.lang=ALL-UNNAMED
+                    </argLine>
                     <systemPropertyVariables>
                         <!-- JaCoCo runtime must know where to dump coverage: -->
                         <jacoco-agent.destfile>target/jacoco.exec</jacoco-agent.destfile>