diff --git a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/GraalHotSpotVMConfig.java b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/GraalHotSpotVMConfig.java
index 555baf10282e..835e4d384aa5 100644
--- a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/GraalHotSpotVMConfig.java
+++ b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/GraalHotSpotVMConfig.java
@@ -239,7 +239,7 @@ public final int logMinObjAlignment() {
     public final int classMirrorOffset = getFieldOffset("Klass::_java_mirror", Integer.class, "OopHandle");
 
     public final int klassSuperKlassOffset = getFieldOffset("Klass::_super", Integer.class, "Klass*");
-    public final int klassModifierFlagsOffset = getFieldOffset("Klass::_modifier_flags", Integer.class, "jint");
+    public final int klassModifierFlagsOffset = getFieldOffset("Klass::_modifier_flags", Integer.class, JDK == 21? "jint" : "u2");
     public final int klassAccessFlagsOffset = getFieldOffset("Klass::_access_flags", Integer.class, "AccessFlags");
     public final int klassMiscFlagsOffset = getFieldOffset("Klass::_misc_flags._flags", Integer.class, "u1", 0, JDK >= 24);
     public final int klassLayoutHelperOffset = getFieldOffset("Klass::_layout_helper", Integer.class, "jint");
diff --git a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/HotSpotInvocationPluginHelper.java b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/HotSpotInvocationPluginHelper.java
index d3c964bc6e88..68ce6d5bf205 100644
--- a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/HotSpotInvocationPluginHelper.java
+++ b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/HotSpotInvocationPluginHelper.java
@@ -52,6 +52,7 @@
 import jdk.graal.compiler.nodes.PiNode;
 import jdk.graal.compiler.nodes.ValueNode;
 import jdk.graal.compiler.nodes.calc.IsNullNode;
+import jdk.graal.compiler.nodes.calc.ZeroExtendNode;
 import jdk.graal.compiler.nodes.extended.GuardingNode;
 import jdk.graal.compiler.nodes.gc.BarrierSet;
 import jdk.graal.compiler.nodes.graphbuilderconf.GraphBuilderContext;
@@ -59,6 +60,7 @@
 import jdk.graal.compiler.nodes.memory.address.AddressNode;
 import jdk.graal.compiler.nodes.type.StampTool;
 import jdk.graal.compiler.replacements.InvocationPluginHelper;
+import jdk.graal.compiler.serviceprovider.JavaVersionUtil;
 import jdk.vm.ci.meta.JavaKind;
 import jdk.vm.ci.meta.ResolvedJavaMethod;
 import jdk.vm.ci.meta.ResolvedJavaType;
@@ -115,7 +117,10 @@ private ValueNode readLocation(ValueNode base, int offset, LocationIdentity loca
      * An abstraction for fields of {@link GraalHotSpotVMConfig}.
      */
     enum HotSpotVMConfigField {
-        KLASS_MODIFIER_FLAGS_OFFSET(config -> config.klassModifierFlagsOffset, KLASS_MODIFIER_FLAGS_LOCATION, StampFactory.forKind(JavaKind.Int)),
+        KLASS_MODIFIER_FLAGS_OFFSET(
+                        config -> config.klassModifierFlagsOffset,
+                        KLASS_MODIFIER_FLAGS_LOCATION,
+                        JavaVersionUtil.JAVA_SPEC == 21 ? StampFactory.forKind(JavaKind.Int) : StampFactory.forInteger(JavaKind.Char.getBitCount())),
         KLASS_SUPER_KLASS_OFFSET(config -> config.klassSuperKlassOffset, KLASS_SUPER_KLASS_LOCATION, KlassPointerStamp.klass()),
         CLASS_ARRAY_KLASS_OFFSET(config -> config.arrayKlassOffset, CLASS_ARRAY_KLASS_LOCATION, KlassPointerStamp.klassNonNull()),
         JAVA_THREAD_OSTHREAD_OFFSET(config -> config.osThreadOffset, JAVA_THREAD_OSTHREAD_LOCATION),
@@ -124,8 +129,14 @@ enum HotSpotVMConfigField {
         /** JavaThread::_threadObj. */
         JAVA_THREAD_CARRIER_THREAD_OBJECT(config -> config.threadCarrierThreadObjectOffset, JAVA_THREAD_CARRIER_THREAD_OBJECT_LOCATION, null),
         JAVA_THREAD_SCOPED_VALUE_CACHE_OFFSET(config -> config.threadScopedValueCacheOffset, JAVA_THREAD_SCOPED_VALUE_CACHE_LOCATION, null),
-        KLASS_ACCESS_FLAGS_OFFSET(config -> config.klassAccessFlagsOffset, KLASS_ACCESS_FLAGS_LOCATION, StampFactory.forKind(JavaKind.Int)),
-        KLASS_MISC_FLAGS_OFFSET(config -> config.klassMiscFlagsOffset, KLASS_MISC_FLAGS_LOCATION, StampFactory.forKind(JavaKind.Int)),
+        KLASS_ACCESS_FLAGS_OFFSET(
+                        config -> config.klassAccessFlagsOffset,
+                        KLASS_ACCESS_FLAGS_LOCATION,
+                        JavaVersionUtil.JAVA_SPEC == 21 ? StampFactory.forKind(JavaKind.Int) : StampFactory.forInteger(JavaKind.Char.getBitCount())),
+        KLASS_MISC_FLAGS_OFFSET(
+                        config -> config.klassMiscFlagsOffset,
+                        KLASS_MISC_FLAGS_LOCATION,
+                        JavaVersionUtil.JAVA_SPEC == 21 ? StampFactory.forKind(JavaKind.Int) : StampFactory.forInteger(JavaKind.Byte.getBitCount())),
         HOTSPOT_OOP_HANDLE_VALUE(config -> 0, HOTSPOT_OOP_HANDLE_LOCATION, StampFactory.forKind(JavaKind.Object));
 
         private final Function<GraalHotSpotVMConfig, Integer> getter;
@@ -162,24 +173,24 @@ public Stamp getStamp(JavaKind wordKind) {
     }
 
     /**
-     * Read {@code Klass::_modifier_flags}.
+     * Read {@code Klass::_modifier_flags} as int.
      */
     public ValueNode readKlassModifierFlags(ValueNode klass) {
-        return readLocation(klass, HotSpotVMConfigField.KLASS_MODIFIER_FLAGS_OFFSET);
+        return ZeroExtendNode.create(readLocation(klass, HotSpotVMConfigField.KLASS_MODIFIER_FLAGS_OFFSET), JavaKind.Int.getBitCount(), NodeView.DEFAULT);
     }
 
     /**
-     * Read {@code Klass::_access_flags}.
+     * Read {@code Klass::_access_flags} as int.
      */
     public ValueNode readKlassAccessFlags(ValueNode klass) {
-        return readLocation(klass, HotSpotVMConfigField.KLASS_ACCESS_FLAGS_OFFSET);
+        return ZeroExtendNode.create(readLocation(klass, HotSpotVMConfigField.KLASS_ACCESS_FLAGS_OFFSET), JavaKind.Int.getBitCount(), NodeView.DEFAULT);
     }
 
     /**
-     * Read {@code Klass::_misc_flags}.
+     * Read {@code Klass::_misc_flags} as int.
      */
     public ValueNode readKlassMiscFlags(ValueNode klass) {
-        return readLocation(klass, HotSpotVMConfigField.KLASS_MISC_FLAGS_OFFSET);
+        return ZeroExtendNode.create(readLocation(klass, HotSpotVMConfigField.KLASS_MISC_FLAGS_OFFSET), JavaKind.Int.getBitCount(), NodeView.DEFAULT);
     }
 
     /**
diff --git a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/MonitorSnippets.java b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/MonitorSnippets.java
index c4c47022b2ab..a3fef028ea61 100644
--- a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/MonitorSnippets.java
+++ b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/MonitorSnippets.java
@@ -231,7 +231,7 @@ public static void monitorenter(Object object, KlassPointer hub, @ConstantParame
         incCounter();
 
         if (diagnoseSyncOnValueBasedClasses(INJECTED_VMCONFIG)) {
-            int flags = shouldUseKlassMiscFlags() ? hub.readInt(klassMiscFlagsOffset(INJECTED_VMCONFIG), KLASS_MISC_FLAGS_LOCATION)
+            int flags = shouldUseKlassMiscFlags() ? hub.readByte(klassMiscFlagsOffset(INJECTED_VMCONFIG), KLASS_MISC_FLAGS_LOCATION)
                             : hub.readInt(klassAccessFlagsOffset(INJECTED_VMCONFIG), KLASS_ACCESS_FLAGS_LOCATION);
             if (probability(SLOW_PATH_PROBABILITY, (flags & jvmAccIsValueBasedClass(INJECTED_VMCONFIG)) != 0)) {
                 monitorenterStubC(MONITORENTER, object, lock);
diff --git a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/RegisterFinalizerSnippets.java b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/RegisterFinalizerSnippets.java
index 60d7505caac1..e77b64cbb6ca 100644
--- a/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/RegisterFinalizerSnippets.java
+++ b/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replacements/RegisterFinalizerSnippets.java
@@ -61,7 +61,7 @@ public class RegisterFinalizerSnippets implements Snippets {
     public static void registerFinalizerSnippet(final Object thisObj) {
         KlassPointer klass = HotSpotReplacementsUtil.loadHub(thisObj);
 
-        int flags = shouldUseKlassMiscFlags() ? klass.readInt(klassMiscFlagsOffset(INJECTED_VMCONFIG), KLASS_MISC_FLAGS_LOCATION)
+        int flags = shouldUseKlassMiscFlags() ? klass.readByte(klassMiscFlagsOffset(INJECTED_VMCONFIG), KLASS_MISC_FLAGS_LOCATION)
                         : klass.readInt(klassAccessFlagsOffset(INJECTED_VMCONFIG), KLASS_ACCESS_FLAGS_LOCATION);
         if (probability(SLOW_PATH_PROBABILITY, (flags & jvmAccHasFinalizer(INJECTED_VMCONFIG)) != 0)) {
             LoweredRegisterFinalizerNode.registerFinalizer(thisObj);
@@ -76,7 +76,8 @@ public static class Templates extends AbstractTemplates {
         public Templates(OptionValues options, HotSpotProviders providers) {
             super(options, providers);
 
-            this.registerFinalizerSnippet = snippet(providers, RegisterFinalizerSnippets.class, "registerFinalizerSnippet", KLASS_ACCESS_FLAGS_LOCATION);
+            this.registerFinalizerSnippet = snippet(providers, RegisterFinalizerSnippets.class, "registerFinalizerSnippet",
+                    shouldUseKlassMiscFlags() ? KLASS_MISC_FLAGS_LOCATION : KLASS_ACCESS_FLAGS_LOCATION);
         }
 
         public void lower(RegisterFinalizerNode node, LoweringTool tool) {