diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorWithResolutionScopes.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorWithResolutionScopes.java
index e8325a222dc..ad0efd0451e 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorWithResolutionScopes.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorWithResolutionScopes.java
@@ -17,6 +17,7 @@
 package org.jetbrains.jet.lang.descriptors;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.resolve.scopes.JetScope;
 
@@ -35,6 +36,10 @@ public interface ClassDescriptorWithResolutionScopes extends ClassDescriptor {
     @NotNull
     JetScope getScopeForMemberLookup();
 
+    @Nullable
+    @Override
+    ClassDescriptorWithResolutionScopes getClassObjectDescriptor();
+
     @NotNull
     @ReadOnly
     Collection<CallableMemberDescriptor> getDeclaredCallableMembers();
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/MutableClassDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/MutableClassDescriptor.java
index 04514d9fd69..8b496a0331a 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/MutableClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/MutableClassDescriptor.java
@@ -44,7 +44,7 @@ public class MutableClassDescriptor extends ClassDescriptorBase implements Class
     private List<TypeParameterDescriptor> typeParameters;
     private Collection<JetType> supertypes = new ArrayList<JetType>();
 
-    private ClassDescriptor classObjectDescriptor;
+    private MutableClassDescriptor classObjectDescriptor;
 
     private final Set<ConstructorDescriptor> constructors = Sets.newLinkedHashSet();
     private ConstructorDescriptor primaryConstructor;
@@ -90,7 +90,7 @@ public class MutableClassDescriptor extends ClassDescriptorBase implements Class
 
     @Nullable
     @Override
-    public ClassDescriptor getClassObjectDescriptor() {
+    public MutableClassDescriptor getClassObjectDescriptor() {
         return classObjectDescriptor;
     }
 
@@ -304,8 +304,8 @@ public class MutableClassDescriptor extends ClassDescriptorBase implements Class
 
     public void lockScopes() {
         getScopeForMemberLookupAsWritableScope().changeLockLevel(WritableScope.LockLevel.READING);
-        if (classObjectDescriptor instanceof MutableClassDescriptor) {
-            ((MutableClassDescriptor) classObjectDescriptor).lockScopes();
+        if (classObjectDescriptor != null) {
+            classObjectDescriptor.lockScopes();
         }
         scopeForSupertypeResolution.changeLockLevel(WritableScope.LockLevel.READING);
         scopeForMemberResolution.changeLockLevel(WritableScope.LockLevel.READING);
@@ -342,7 +342,7 @@ public class MutableClassDescriptor extends ClassDescriptorBase implements Class
                 }
 
                 @Override
-                public ClassObjectStatus setClassObjectDescriptor(@NotNull ClassDescriptor classObjectDescriptor) {
+                public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor) {
                     if (getKind() == ClassKind.CLASS_OBJECT || isInner()) {
                         return ClassObjectStatus.NOT_ALLOWED;
                     }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilder.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilder.java
index a4cda695b60..7478999acc8 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilder.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilder.java
@@ -17,7 +17,6 @@
 package org.jetbrains.jet.lang.descriptors.impl;
 
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
 import org.jetbrains.jet.lang.descriptors.PropertyDescriptor;
 import org.jetbrains.jet.lang.descriptors.SimpleFunctionDescriptor;
@@ -38,5 +37,5 @@ public interface PackageLikeBuilder {
         NOT_ALLOWED
     }
 
-    ClassObjectStatus setClassObjectDescriptor(@NotNull ClassDescriptor classObjectDescriptor);
+    ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor);
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilderDummy.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilderDummy.java
index 7c278df932e..f64f02f74c4 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilderDummy.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/PackageLikeBuilderDummy.java
@@ -17,7 +17,6 @@
 package org.jetbrains.jet.lang.descriptors.impl;
 
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
 import org.jetbrains.jet.lang.descriptors.PropertyDescriptor;
 import org.jetbrains.jet.lang.descriptors.SimpleFunctionDescriptor;
@@ -45,7 +44,7 @@ public class PackageLikeBuilderDummy implements PackageLikeBuilder {
     }
 
     @Override
-    public ClassObjectStatus setClassObjectDescriptor(@NotNull ClassDescriptor classObjectDescriptor) {
+    public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor) {
         throw new IllegalStateException();
     }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/ScopeBasedPackageLikeBuilder.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/ScopeBasedPackageLikeBuilder.java
index 3234fa4cfe4..973ce2efa5a 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/ScopeBasedPackageLikeBuilder.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/impl/ScopeBasedPackageLikeBuilder.java
@@ -17,7 +17,6 @@
 package org.jetbrains.jet.lang.descriptors.impl;
 
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
 import org.jetbrains.jet.lang.descriptors.PropertyDescriptor;
 import org.jetbrains.jet.lang.descriptors.SimpleFunctionDescriptor;
@@ -57,7 +56,7 @@ public class ScopeBasedPackageLikeBuilder implements PackageLikeBuilder {
     }
 
     @Override
-    public ClassObjectStatus setClassObjectDescriptor(@NotNull ClassDescriptor classObjectDescriptor) {
+    public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor) {
         throw new IllegalStateException("Must be guaranteed not to happen by the parser");
     }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/DeclarationResolver.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/DeclarationResolver.java
index 782d1cd3ce3..276a5d9070e 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/DeclarationResolver.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/DeclarationResolver.java
@@ -347,10 +347,9 @@ public class DeclarationResolver {
 
             Collection<DeclarationDescriptor> allDescriptors = classDescriptor.getScopeForMemberLookup().getOwnDeclaredDescriptors();
 
-            ClassDescriptor classObj = classDescriptor.getClassObjectDescriptor();
-            if (classObj instanceof ClassDescriptorWithResolutionScopes) {
-                Collection<DeclarationDescriptor> classObjDescriptors =
-                        ((ClassDescriptorWithResolutionScopes) classObj).getScopeForMemberLookup().getOwnDeclaredDescriptors();
+            ClassDescriptorWithResolutionScopes classObj = classDescriptor.getClassObjectDescriptor();
+            if (classObj != null) {
+                Collection<DeclarationDescriptor> classObjDescriptors = classObj.getScopeForMemberLookup().getOwnDeclaredDescriptors();
                 if (!classObjDescriptors.isEmpty()) {
                     allDescriptors = Lists.newArrayList(allDescriptors);
                     allDescriptors.addAll(classObjDescriptors);
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java
index cd377154725..032eb8f8d6e 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java
@@ -85,9 +85,9 @@ public class OverrideResolver {
             if (ourClasses.contains(klass)) {
                 generateOverridesAndDelegationInAClass(klass, processed, ourClasses);
 
-                ClassDescriptor classObject = klass.getClassObjectDescriptor();
-                if (classObject instanceof MutableClassDescriptor) {
-                    generateOverridesAndDelegationInAClass((MutableClassDescriptor) classObject, processed, ourClasses);
+                MutableClassDescriptor classObject = klass.getClassObjectDescriptor();
+                if (classObject != null) {
+                    generateOverridesAndDelegationInAClass(classObject, processed, ourClasses);
                 }
             }
         }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
index 9008a973940..a157c2527b2 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
@@ -238,7 +238,7 @@ public class TopDownAnalyzer {
                    }
 
                    @Override
-                   public ClassObjectStatus setClassObjectDescriptor(@NotNull ClassDescriptor classObjectDescriptor) {
+                   public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor) {
                        return ClassObjectStatus.NOT_ALLOWED;
                    }
                },
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java
index 1e7a430e4f7..0470b9e626e 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java
@@ -204,7 +204,7 @@ public class TypeHierarchyResolver {
 
             ClassKind kind = descriptor.getKind();
             if (kind == ClassKind.ENUM_ENTRY || kind == ClassKind.OBJECT) {
-                MutableClassDescriptor classObject = (MutableClassDescriptor) descriptor.getClassObjectDescriptor();
+                MutableClassDescriptor classObject = descriptor.getClassObjectDescriptor();
                 assert classObject != null : "Enum entries and named objects should have class objects: " + classOrObject.getText();
 
                 // This is a clever hack: each enum entry and object declaration (i.e. singleton) has a synthetic class object.
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/descriptors/LazyClassDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/descriptors/LazyClassDescriptor.java
index b62d93e6dbe..c53addf5d8f 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/descriptors/LazyClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/descriptors/LazyClassDescriptor.java
@@ -83,7 +83,7 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
     private final boolean isInner;
 
     private final Annotations annotations;
-    private final NullableLazyValue<ClassDescriptor> classObjectDescriptor;
+    private final NullableLazyValue<LazyClassDescriptor> classObjectDescriptor;
     private final MemoizedFunctionToNotNull<JetClassObject, ClassDescriptor> extraClassObjectDescriptors;
 
     private final LazyClassMemberScope unsubstitutedMemberScope;
@@ -158,9 +158,9 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
             this.annotations = Annotations.EMPTY;
         }
 
-        this.classObjectDescriptor = storageManager.createNullableLazyValue(new Function0<ClassDescriptor>() {
+        this.classObjectDescriptor = storageManager.createNullableLazyValue(new Function0<LazyClassDescriptor>() {
             @Override
-            public ClassDescriptor invoke() {
+            public LazyClassDescriptor invoke() {
                 return computeClassObjectDescriptor(declarationProvider.getOwnerInfo().getClassObject());
             }
         });
@@ -324,7 +324,7 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
     }
 
     @Override
-    public ClassDescriptor getClassObjectDescriptor() {
+    public LazyClassDescriptor getClassObjectDescriptor() {
         return classObjectDescriptor.invoke();
     }
 
@@ -351,7 +351,7 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
     }
 
     @Nullable
-    private ClassDescriptor computeClassObjectDescriptor(@Nullable JetClassObject classObject) {
+    private LazyClassDescriptor computeClassObjectDescriptor(@Nullable JetClassObject classObject) {
         JetClassLikeInfo classObjectInfo = getClassObjectInfo(classObject);
         if (classObjectInfo != null) {
             return new LazyClassDescriptor(resolveSession, this, getClassObjectName(getName()), classObjectInfo);