diff --git a/src/main/java/com/android/tools/r8/graph/ClassAccessFlags.java b/src/main/java/com/android/tools/r8/graph/ClassAccessFlags.java
index dba763b..888f1e8 100644
--- a/src/main/java/com/android/tools/r8/graph/ClassAccessFlags.java
+++ b/src/main/java/com/android/tools/r8/graph/ClassAccessFlags.java
@@ -184,6 +184,10 @@
     set(Constants.ACC_ENUM);
   }
 
+  public void unsetEnum() {
+    unset(Constants.ACC_ENUM);
+  }
+
   public boolean isRecord() {
     return isSet(Constants.ACC_RECORD);
   }
diff --git a/src/main/java/com/android/tools/r8/graph/ObjectAllocationInfoCollectionImpl.java b/src/main/java/com/android/tools/r8/graph/ObjectAllocationInfoCollectionImpl.java
index aea1754..40b16d7 100644
--- a/src/main/java/com/android/tools/r8/graph/ObjectAllocationInfoCollectionImpl.java
+++ b/src/main/java/com/android/tools/r8/graph/ObjectAllocationInfoCollectionImpl.java
@@ -488,7 +488,6 @@
           (clazz, allocationSitesForClass) -> {
             DexType type = lens.lookupType(clazz.type);
             if (type.isPrimitiveType()) {
-              assert clazz.isEnum();
               return;
             }
             DexProgramClass rewrittenClass = asProgramClassOrNull(definitions.definitionFor(type));
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxerImpl.java b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxerImpl.java
index 4ca2bb2..9110440 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxerImpl.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxerImpl.java
@@ -1376,12 +1376,12 @@
     DexClassAndMethod mostAccurateTarget = singleTarget == null ? resolvedMethod : singleTarget;
 
     if (mostAccurateTarget.isProgramMethod()) {
-      if (mostAccurateTarget.getHolder().isEnum()
-          && resolvedMethod.getDefinition().isInstanceInitializer()) {
+      DexProgramClass candidateOrNull =
+          getEnumUnboxingCandidateOrNull(mostAccurateTarget.getHolderType());
+      if (candidateOrNull != null && resolvedMethod.getDefinition().isInstanceInitializer()) {
         // The enum instance initializer is only allowed to be called from an initializer of the
         // enum itself.
-        if (getEnumUnboxingCandidateOrNull(code.context().getHolderType())
-                != getEnumUnboxingCandidateOrNull(mostAccurateTarget.getHolderType())
+        if (getEnumUnboxingCandidateOrNull(code.context().getHolderType()) != candidateOrNull
             || !context.getDefinition().isInitializer()) {
           return Reason.INVALID_INIT;
         }
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateAnalysis.java b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateAnalysis.java
index 4531523..faec94c 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateAnalysis.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateAnalysis.java
@@ -4,7 +4,6 @@
 
 package com.android.tools.r8.ir.optimize.enums;
 
-import static com.android.tools.r8.utils.MapUtils.ignoreKey;
 
 import com.android.tools.r8.graph.AppView;
 import com.android.tools.r8.graph.DexClass;
@@ -14,16 +13,14 @@
 import com.android.tools.r8.graph.DexProgramClass;
 import com.android.tools.r8.graph.DexProto;
 import com.android.tools.r8.graph.DexType;
+import com.android.tools.r8.graph.ImmediateProgramSubtypingInfo;
 import com.android.tools.r8.graph.lens.GraphLens;
 import com.android.tools.r8.ir.optimize.enums.eligibility.Reason;
 import com.android.tools.r8.shaking.AppInfoWithLiveness;
 import com.android.tools.r8.shaking.KeepInfoCollection;
 import com.android.tools.r8.utils.InternalOptions;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Sets;
-import java.util.IdentityHashMap;
-import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 class EnumUnboxingCandidateAnalysis {
 
@@ -35,12 +32,9 @@
   private final AppView<AppInfoWithLiveness> appView;
   private final EnumUnboxerImpl enumUnboxer;
   private final DexItemFactory factory;
-  private EnumUnboxingCandidateInfoCollection enumToUnboxCandidates =
+  private final EnumUnboxingCandidateInfoCollection enumToUnboxCandidates =
       new EnumUnboxingCandidateInfoCollection();
 
-  private final Map<DexType, Set<DexProgramClass>> enumSubclasses = new IdentityHashMap<>();
-  private final Set<DexType> ineligibleCandidates = Sets.newIdentityHashSet();
-
   EnumUnboxingCandidateAnalysis(AppView<AppInfoWithLiveness> appView, EnumUnboxerImpl enumUnboxer) {
     this.appView = appView;
     this.enumUnboxer = enumUnboxer;
@@ -54,13 +48,13 @@
       // disables the enum unboxer.
       return enumToUnboxCandidates;
     }
+    ImmediateProgramSubtypingInfo subtypingInfo = ImmediateProgramSubtypingInfo.create(appView);
+    // In recent Kotlin enum subclasses are not flagged as enum, so we cannot rely on the flag.
     for (DexProgramClass clazz : appView.appInfo().classes()) {
-      if (clazz.isEnum()) {
-        analyzeEnum(graphLensForPrimaryOptimizationPass, clazz);
+      if (clazz.isEnum() && clazz.superType == factory.enumType) {
+        analyzeEnum(graphLensForPrimaryOptimizationPass, clazz, subtypingInfo);
       }
     }
-    removeIneligibleCandidates();
-    setEnumSubclassesOnCandidates();
     removeEnumsInAnnotations();
     removePinnedCandidates();
     if (appView.options().protoShrinking().isProtoShrinkingEnabled()) {
@@ -70,40 +64,27 @@
     return enumToUnboxCandidates;
   }
 
-  private void setEnumSubclassesOnCandidates() {
-    enumToUnboxCandidates.forEachCandidateInfo(
-        info -> {
-          DexType type = info.getEnumClass().getType();
-          enumToUnboxCandidates.setEnumSubclasses(
-              type, enumSubclasses.getOrDefault(type, ImmutableSet.of()));
-        });
-  }
-
-  private void removeIneligibleCandidates() {
-    for (DexType ineligibleCandidate : ineligibleCandidates) {
-      enumToUnboxCandidates.removeCandidate(ineligibleCandidate);
+  private void analyzeEnum(
+      GraphLens graphLensForPrimaryOptimizationPass,
+      DexProgramClass clazz,
+      ImmediateProgramSubtypingInfo subtypingInfo) {
+    if (!isSuperEnumUnboxingCandidate(clazz)) {
+      return;
     }
-  }
 
-  private void analyzeEnum(GraphLens graphLensForPrimaryOptimizationPass, DexProgramClass clazz) {
-    if (clazz.superType == factory.enumType) {
-      if (isSuperEnumUnboxingCandidate(clazz)) {
-        enumToUnboxCandidates.addCandidate(appView, clazz, graphLensForPrimaryOptimizationPass);
+    List<DexProgramClass> subtypes = subtypingInfo.getSubclasses(clazz);
+    ImmutableSet.Builder<DexProgramClass> subEnumClassesBuilder = ImmutableSet.builder();
+    for (DexProgramClass subEnum : subtypes) {
+      if (!isSubEnumUnboxingCandidate(subEnum)) {
+        return;
       }
-    } else {
-      if (isSubEnumUnboxingCandidate(clazz)
-          && appView.options().testing.enableEnumWithSubtypesUnboxing) {
-        enumSubclasses
-            .computeIfAbsent(clazz.superType, ignoreKey(Sets::newIdentityHashSet))
-            .add(clazz);
-      } else {
-        ineligibleCandidates.add(clazz.superType);
-      }
+      subEnumClassesBuilder.add(subEnum);
     }
+    enumToUnboxCandidates.addCandidate(
+        appView, clazz, subEnumClassesBuilder.build(), graphLensForPrimaryOptimizationPass);
   }
 
   private boolean isSubEnumUnboxingCandidate(DexProgramClass clazz) {
-    assert clazz.isEnum();
     boolean result = true;
     // Javac does not seem to generate enums with more than a single subtype level.
     // TODO(b/273910479): Stop using isEffectivelyFinal.
@@ -132,26 +113,12 @@
 
   private boolean isSuperEnumUnboxingCandidate(DexProgramClass clazz) {
     assert clazz.isEnum();
-
-    // This is used in debug mode, where we don't do quick returns to log all the reasons an enum
-    // is not unboxed.
-    boolean result = true;
-
-    // TODO(b/271385332): Change this into an assert when legacy is removed.
-    if (clazz.superType != factory.enumType) {
-      if (!enumUnboxer.reportFailure(clazz, Reason.INVALID_LIBRARY_SUPERTYPE)) {
-        return false;
-      }
-      result = false;
-    }
-
+    assert clazz.superType == factory.enumType;
     if (clazz.instanceFields().size() > MAX_INSTANCE_FIELDS_FOR_UNBOXING) {
-      if (!enumUnboxer.reportFailure(clazz, Reason.MANY_INSTANCE_FIELDS)) {
-        return false;
-      }
-      result = false;
+      enumUnboxer.reportFailure(clazz, Reason.MANY_INSTANCE_FIELDS);
+      return false;
     }
-    return result;
+    return true;
   }
 
   private void removeEnumsInAnnotations() {
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateInfoCollection.java b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateInfoCollection.java
index 06cf453..809147b 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateInfoCollection.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/enums/EnumUnboxingCandidateInfoCollection.java
@@ -35,11 +35,16 @@
   public void addCandidate(
       AppView<AppInfoWithLiveness> appView,
       DexProgramClass enumClass,
+      Set<DexProgramClass> subclasses,
       GraphLens graphLensForPrimaryOptimizationPass) {
     assert !enumTypeToInfo.containsKey(enumClass.type);
     enumTypeToInfo.put(
         enumClass.type,
-        new EnumUnboxingCandidateInfo(appView, enumClass, graphLensForPrimaryOptimizationPass));
+        new EnumUnboxingCandidateInfo(
+            appView, enumClass, subclasses, graphLensForPrimaryOptimizationPass));
+    for (DexProgramClass subclass : subclasses) {
+      subEnumToSuperEnumMap.put(subclass.getType(), enumClass.getType());
+    }
   }
 
   public boolean hasSubtypes(DexType enumType) {
@@ -51,13 +56,6 @@
         enumTypeToInfo.get(enumType).getSubclasses(), DexClass::getType);
   }
 
-  public void setEnumSubclasses(DexType superEnum, Set<DexProgramClass> subclasses) {
-    enumTypeToInfo.get(superEnum).setSubclasses(subclasses);
-    for (DexProgramClass subclass : subclasses) {
-      subEnumToSuperEnumMap.put(subclass.getType(), superEnum);
-    }
-  }
-
   public void addPrunedMethod(ProgramMethod method) {
     prunedMethods.add(method.getReference());
   }
@@ -174,10 +172,12 @@
     public EnumUnboxingCandidateInfo(
         AppView<AppInfoWithLiveness> appView,
         DexProgramClass enumClass,
+        Set<DexProgramClass> subclasses,
         GraphLens graphLensForPrimaryOptimizationPass) {
       assert enumClass != null;
       assert appView.graphLens() == graphLensForPrimaryOptimizationPass;
       this.enumClass = enumClass;
+      this.subclasses = subclasses;
       this.methodDependencies =
           LongLivedProgramMethodSetBuilder.createConcurrentForIdentitySet(
               graphLensForPrimaryOptimizationPass);
@@ -188,10 +188,6 @@
       return subclasses;
     }
 
-    public void setSubclasses(Set<DexProgramClass> subclasses) {
-      this.subclasses = subclasses;
-    }
-
     public DexProgramClass getEnumClass() {
       return enumClass;
     }
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/enums/eligibility/Reason.java b/src/main/java/com/android/tools/r8/ir/optimize/enums/eligibility/Reason.java
index 56b05f6..3cf50f1 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/enums/eligibility/Reason.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/enums/eligibility/Reason.java
@@ -11,18 +11,13 @@
 
 public abstract class Reason {
   public static final Reason ELIGIBLE = new StringReason("ELIGIBLE");
-  public static final Reason ACCESSIBILITY = new StringReason("ACCESSIBILITY");
   public static final Reason ANNOTATION = new StringReason("ANNOTATION");
   public static final Reason PINNED = new StringReason("PINNED");
   public static final Reason DOWN_CAST = new StringReason("DOWN_CAST");
-  public static final Reason INVALID_LIBRARY_SUPERTYPE =
-      new StringReason("INVALID_LIBRARY_SUPERTYPE");
-  public static final Reason SUBTYPES = new StringReason("SUBTYPES");
   public static final Reason SUBENUM_SUBTYPES = new StringReason("SUBENUM_SUBTYPES");
   public static final Reason SUBENUM_INVALID_HIERARCHY =
       new StringReason("SUBENUM_INVALID_HIERARCHY");
   public static final Reason SUBENUM_INSTANCE_FIELDS = new StringReason("SUBENUM_INSTANCE_FIELDS");
-  public static final Reason SUBENUM_STATIC_MEMBER = new StringReason("SUBENUM_STATIC_MEMBER");
   public static final Reason MANY_INSTANCE_FIELDS = new StringReason("MANY_INSTANCE_FIELDS");
   public static final Reason DEFAULT_METHOD_INVOKE = new StringReason("DEFAULT_METHOD_INVOKE");
   public static final Reason UNRESOLVABLE_FIELD = new StringReason("UNRESOLVABLE_FIELD");
diff --git a/src/main/java/com/android/tools/r8/utils/InternalOptions.java b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
index b0d3c73..e00912a 100644
--- a/src/main/java/com/android/tools/r8/utils/InternalOptions.java
+++ b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
@@ -2333,7 +2333,7 @@
     public boolean enableSwitchToIfRewriting = true;
     public boolean enableEnumUnboxingDebugLogs =
         System.getProperty("com.android.tools.r8.enableEnumUnboxingDebugLogs") != null;
-    public boolean enableEnumWithSubtypesUnboxing = true;
+    public boolean enableVerticalClassMergerLensAssertion = false;
     public boolean forceRedundantConstNumberRemoval = false;
     public boolean enableExperimentalDesugaredLibraryKeepRuleGenerator = false;
     public boolean invertConditionals = false;
diff --git a/src/test/java/com/android/tools/r8/enumunboxing/enummerging/BasicEnumMergingKeepSubtypeTest.java b/src/test/java/com/android/tools/r8/enumunboxing/enummerging/BasicEnumMergingKeepSubtypeTest.java
index 4f1d44e..c2446e9 100644
--- a/src/test/java/com/android/tools/r8/enumunboxing/enummerging/BasicEnumMergingKeepSubtypeTest.java
+++ b/src/test/java/com/android/tools/r8/enumunboxing/enummerging/BasicEnumMergingKeepSubtypeTest.java
@@ -42,7 +42,6 @@
         .addKeepMainRule(Main.class)
         .addKeepRules("-keep class " + SUBTYPE_NAME + " { public void method(); }")
         .addKeepRules(enumKeepRules.getKeepRules())
-        .addOptionsModification(opt -> opt.testing.enableEnumWithSubtypesUnboxing = true)
         .addEnumUnboxingInspector(
             inspector -> inspector.assertNotUnboxed(EnumWithVirtualOverride.class))
         .addOptionsModification(opt -> enableEnumOptions(opt, enumValueOptimization))
diff --git a/src/test/java/com/android/tools/r8/enumunboxing/enummerging/NoEnumFlagEnumMergingTest.java b/src/test/java/com/android/tools/r8/enumunboxing/enummerging/NoEnumFlagEnumMergingTest.java
new file mode 100644
index 0000000..61df4af
--- /dev/null
+++ b/src/test/java/com/android/tools/r8/enumunboxing/enummerging/NoEnumFlagEnumMergingTest.java
@@ -0,0 +1,127 @@
+// Copyright (c) 2023, the R8 project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+package com.android.tools.r8.enumunboxing.enummerging;
+
+import com.android.tools.r8.NeverInline;
+import com.android.tools.r8.TestParameters;
+import com.android.tools.r8.ToolHelper;
+import com.android.tools.r8.enumunboxing.EnumUnboxingTestBase;
+import com.android.tools.r8.graph.ClassAccessFlags;
+import com.android.tools.r8.references.Reference;
+import com.android.tools.r8.utils.DescriptorUtils;
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.stream.Collectors;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class NoEnumFlagEnumMergingTest extends EnumUnboxingTestBase {
+
+  private final TestParameters parameters;
+  private final boolean enumValueOptimization;
+  private final EnumKeepRules enumKeepRules;
+
+  @Parameters(name = "{0} valueOpt: {1} keep: {2}")
+  public static List<Object[]> data() {
+    return enumUnboxingTestParameters();
+  }
+
+  public NoEnumFlagEnumMergingTest(
+      TestParameters parameters, boolean enumValueOptimization, EnumKeepRules enumKeepRules) {
+    this.parameters = parameters;
+    this.enumValueOptimization = enumValueOptimization;
+    this.enumKeepRules = enumKeepRules;
+  }
+
+  @Test
+  public void testEnumUnboxing() throws Exception {
+    testForR8(parameters.getBackend())
+        .addProgramFiles(getEnumSubtypesOrOtherInputs(false))
+        .addProgramClassFileData(getSubEnumProgramData(getEnumSubtypesOrOtherInputs(true)))
+        .addKeepMainRule(Main.class)
+        .addKeepRules(enumKeepRules.getKeepRules())
+        .addEnumUnboxingInspector(inspector -> inspector.assertUnboxed(MyEnum2Cases.class))
+        .enableInliningAnnotations()
+        .addOptionsModification(opt -> enableEnumOptions(opt, enumValueOptimization))
+        .setMinApi(parameters)
+        .run(parameters.getRuntime(), Main.class)
+        .assertSuccessWithOutputLines("336", "74", "96", "44");
+  }
+
+  private List<Path> getEnumSubtypesOrOtherInputs(boolean enumSubtypes) throws IOException {
+    return ToolHelper.getClassFilesForInnerClasses(getClass()).stream()
+        .filter(path -> isMyEnum2CasesSubtype(path) == enumSubtypes)
+        .collect(Collectors.toList());
+  }
+
+  private boolean isMyEnum2CasesSubtype(Path c) {
+    return c.toString().contains("MyEnum2Cases") && !c.toString().endsWith("MyEnum2Cases.class");
+  }
+
+  private List<byte[]> getSubEnumProgramData(List<Path> input) {
+    // Some Kotlin enum subclasses don't have the enum flag set. See b/315186101.
+    return input.stream()
+        .map(
+            path -> {
+              try {
+                String subtype = path.getFileName().toString();
+                String subtypeNoClass =
+                    subtype.substring(0, (subtype.length() - ".class".length()));
+                String descr =
+                    DescriptorUtils.replaceSimpleClassNameInDescriptor(
+                        DescriptorUtils.javaTypeToDescriptor(MyEnum2Cases.class.getTypeName()),
+                        subtypeNoClass);
+                return transformer(path, Reference.classFromDescriptor(descr))
+                    .setAccessFlags(ClassAccessFlags::unsetEnum)
+                    .transform();
+              } catch (IOException e) {
+                throw new RuntimeException(e);
+              }
+            })
+        .collect(Collectors.toList());
+  }
+
+  enum MyEnum2Cases {
+    A(8) {
+      @NeverInline
+      @Override
+      public long operate(long another) {
+        return num * another;
+      }
+    },
+    B(32) {
+      @NeverInline
+      @Override
+      public long operate(long another) {
+        return num + another;
+      }
+    };
+    final long num;
+
+    MyEnum2Cases(long num) {
+      this.num = num;
+    }
+
+    public abstract long operate(long another);
+  }
+
+  static class Main {
+
+    public static void main(String[] args) {
+      System.out.println(MyEnum2Cases.A.operate(42));
+      System.out.println(MyEnum2Cases.B.operate(42));
+      System.out.println(indirect(MyEnum2Cases.A));
+      System.out.println(indirect(MyEnum2Cases.B));
+    }
+
+    @NeverInline
+    public static long indirect(MyEnum2Cases e) {
+      return e.operate(12);
+    }
+  }
+}