diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 4f2fcc7..0c36f2a 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -23,8 +23,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # 26-Sep-2025, tatu: some test failures on 21 cannot yet enable
-        java_version: ['8', '11', '17']
+        java_version: ['8', '17', '21', '25']
     env:
       JAVA_OPTS: "-XX:+TieredCompilation -XX:TieredStopAtLevel=1"
     steps:
diff --git a/src/test/java/com/fasterxml/classmate/AnnotationsTest.java b/src/test/java/com/fasterxml/classmate/AnnotationsTest.java
index 096bed3..6b0a49e 100644
--- a/src/test/java/com/fasterxml/classmate/AnnotationsTest.java
+++ b/src/test/java/com/fasterxml/classmate/AnnotationsTest.java
@@ -7,17 +7,15 @@
 import java.lang.annotation.RetentionPolicy;
 import java.lang.reflect.Method;
 
-import static junit.framework.Assert.*;
-import static org.junit.Assert.assertEquals;
-
-@SuppressWarnings("deprecation")
-public class AnnotationsTest {
+import static org.junit.Assert.*;
 
+public class AnnotationsTest
+{
     @Retention(RetentionPolicy.RUNTIME)
     private static @interface Marker { }
 
     @Test @Marker
-    public void addAsDefault() throws NoSuchMethodException {
+    public void addAsDefault() throws Exception {
         Annotations annotations = new Annotations();
         Method thisMethod = AnnotationsTest.class.getDeclaredMethod("addAsDefault");
 
@@ -39,7 +37,7 @@ public void addAsDefault() throws NoSuchMethodException {
     }
 
     @Test
-    public void size() throws NoSuchMethodException {
+    public void size() throws Exception {
         Annotations annotations = new Annotations();
         Method thisMethod = AnnotationsTest.class.getDeclaredMethod("addAsDefault");
 
@@ -57,7 +55,7 @@ public void size() throws NoSuchMethodException {
     }
 
     @Test
-    public void annotationsToSize() throws NoSuchMethodException {
+    public void annotationsToSize() throws Exception {
         Annotations annotations = new Annotations();
         Method thisMethod = AnnotationsTest.class.getDeclaredMethod("addAsDefault");
 
@@ -67,23 +65,42 @@ public void annotationsToSize() throws NoSuchMethodException {
         annotations.addAsDefault(testAnnotation);
 
         // order is unspecified as the internal representation is a HashMap; just assert the constituent parts are present
-        String asString = annotations.toString();
+        String asString = _normalize(annotations.toString());
         assertTrue(asString.contains("{interface org.junit.Test=@org.junit.Test("));
         assertTrue(asString.contains("timeout=0"));
 
         // 15-Nov-2016, tatu: Java 9 changes description slightly, need to modify
-        assertTrue(asString.contains("expected=class org.junit.Test$None") // until Java 8
-                || asString.contains("expected=org.junit.Test$None"));
+        // 05-Dec-2025, tatu: Java 21 adds further variation
+        if (!(asString.contains("expected=class org.junit.Test.None") // until Java 8
+                || asString.contains("expected=org.junit.Test.None"))) {
+            fail("No 'expected' in: "+asString);
+        }
 
         Annotation markerAnnotation = thisMethod.getAnnotation(Marker.class);
         annotations.addAsDefault(markerAnnotation);
 
-        asString = annotations.toString();
-        assertTrue(asString.contains("interface com.fasterxml.classmate.AnnotationsTest$Marker=@com.fasterxml.classmate.AnnotationsTest$Marker()"));
+        asString = _normalize(annotations.toString());
+
+        String exp = "interface com.fasterxml.classmate.AnnotationsTest.Marker=@com.fasterxml.classmate.AnnotationsTest.Marker()";
+        if (!asString.contains(exp)) {
+            fail("Expected: ["+exp+"]\nin ["+asString+"]");
+        }
         assertTrue(asString.contains("interface org.junit.Test=@org.junit.Test"));
         assertTrue(asString.contains("timeout=0"));
         // 15-Nov-2016, tatu: Java 9 changes description slightly, need to modify
-        assertTrue(asString.contains("expected=class org.junit.Test$None")
-                || asString.contains("expected=org.junit.Test$None"));
+        // 05-Dec-2025, tatu: Java 21 adds further variation
+        if (!(asString.contains("expected=class org.junit.Test.None") // until Java 8
+                || asString.contains("expected=org.junit.Test.None"))) {
+            fail("No 'expected' in: "+asString);
+        }
+    }
+
+    private static String _normalize(String str) {
+        // 05-Dec-2025, tatu: Java 21 changes from "org.junit.Test$None" to "org.junit.Test.None"
+        String str2;
+        while ((str2 = str.replace('$', '.')) != str) {
+            str = str2;
+        }
+        return str;
     }
 }
diff --git a/src/test/java/com/fasterxml/classmate/TestMemberResolver.java b/src/test/java/com/fasterxml/classmate/MemberResolverTest.java
similarity index 93%
rename from src/test/java/com/fasterxml/classmate/TestMemberResolver.java
rename to src/test/java/com/fasterxml/classmate/MemberResolverTest.java
index 50c6442..bd05ae6 100644
--- a/src/test/java/com/fasterxml/classmate/TestMemberResolver.java
+++ b/src/test/java/com/fasterxml/classmate/MemberResolverTest.java
@@ -8,7 +8,7 @@
 import com.fasterxml.classmate.types.ResolvedObjectType;
 import com.fasterxml.classmate.util.ClassKey;
 
-public class TestMemberResolver extends BaseTest
+public class MemberResolverTest extends BaseTest
 {
     /*
     /**********************************************************************
@@ -214,7 +214,11 @@ public void testIncludeObject()
         mr.setIncludeLangObject(true);
 
         simpleResolvedTypeWithMembers = mr.resolve(simpleResolvedType, null, null);
-        assertEquals(12, simpleResolvedTypeWithMembers.getMemberMethods().length);
+        // With JDK < 21, 12 member methods, 21+ 13
+        int methodCount = simpleResolvedTypeWithMembers.getMemberMethods().length;
+        if (methodCount < 12 || methodCount > 13) {
+            fail("Expected [12, 13] methods, got: "+methodCount);
+        }
         assertEquals(1, simpleResolvedTypeWithMembers.getMemberFields().length);
     }
 
@@ -225,7 +229,12 @@ public void testFilters()
         mr.setIncludeLangObject(true);
 
         ResolvedTypeWithMembers simpleResolvedTypeWithMembers = mr.resolve(simpleResolvedType, null, null);
-        assertEquals(12, simpleResolvedTypeWithMembers.getMemberMethods().length);
+        // With JDK < 21, 12 member methods, 21+ 13
+        int methodCount = simpleResolvedTypeWithMembers.getMemberMethods().length;
+        if (methodCount < 12 || methodCount > 13) {
+            fail("Expected [12, 13] methods, got: "+methodCount);
+        }
+
         assertEquals(1, simpleResolvedTypeWithMembers.getMemberFields().length);
         assertEquals(2, simpleResolvedTypeWithMembers.getConstructors().length);
 
@@ -253,7 +262,12 @@ public void testFilters()
         });
 
         simpleResolvedTypeWithMembers = mr.resolve(simpleResolvedType, null, null);
-        assertEquals(12, simpleResolvedTypeWithMembers.getMemberMethods().length);
+
+        // With JDK < 21, 12 member methods, 21+ 13
+        methodCount = simpleResolvedTypeWithMembers.getMemberMethods().length;
+        if (methodCount < 12 || methodCount > 13) {
+            fail("Expected [12, 13] methods, got: "+methodCount);
+        }
         assertEquals(0, simpleResolvedTypeWithMembers.getMemberFields().length);
         assertEquals(2, simpleResolvedTypeWithMembers.getConstructors().length);
 
@@ -267,7 +281,11 @@ public void testFilters()
         });
 
         simpleResolvedTypeWithMembers = mr.resolve(simpleResolvedType, null, null);
-        assertEquals(12, simpleResolvedTypeWithMembers.getMemberMethods().length);
+        // With JDK < 21, 12 member methods, 21+ 13
+        methodCount = simpleResolvedTypeWithMembers.getMemberMethods().length;
+        if (methodCount < 12 || methodCount > 13) {
+            fail("Expected [12, 13] methods, got: "+methodCount);
+        }
         assertEquals(1, simpleResolvedTypeWithMembers.getMemberFields().length);
         assertEquals(1, simpleResolvedTypeWithMembers.getConstructors().length);
     }