diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/MutableClassDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/MutableClassDescriptor.java
index 2368a139319..4343f270286 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/MutableClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/MutableClassDescriptor.java
@@ -28,7 +28,7 @@ public class MutableClassDescriptor extends MutableDeclarationDescriptor impleme
     private final Set<CallableMemberDescriptor> callableMembers = Sets.newHashSet();
     private final Set<PropertyDescriptor> properties = Sets.newHashSet();
     private final Set<NamedFunctionDescriptor> functions = Sets.newHashSet();
-    private List<TypeParameterDescriptor> typeParameters = Lists.newArrayList();
+    private List<TypeParameterDescriptor> typeParameters;
     private Collection<JetType> supertypes = Lists.newArrayList();
     private Map<String, ClassDescriptor> innerClassesAndObjects = Maps.newHashMap();
 
@@ -217,6 +217,10 @@ public class MutableClassDescriptor extends MutableDeclarationDescriptor impleme
     }
 
     public void setTypeParameterDescriptors(List<TypeParameterDescriptor> typeParameters) {
+        if (this.typeParameters != null) {
+            throw new IllegalStateException();
+        }
+        this.typeParameters = new ArrayList<TypeParameterDescriptor>();
         for (TypeParameterDescriptor typeParameterDescriptor : typeParameters) {
             this.typeParameters.add(typeParameterDescriptor);
             scopeForSupertypeResolution.addTypeParameterDescriptor(typeParameterDescriptor);
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 4c797de0114..852cf89e6f8 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/TypeHierarchyResolver.java
@@ -94,6 +94,7 @@ public class TypeHierarchyResolver {
                         classObjectDescriptor.setName("class-object-for-" + klass.getName());
                         classObjectDescriptor.setModality(Modality.FINAL);
                         classObjectDescriptor.setVisibility(DescriptorResolver.resolveVisibilityFromModifiers(klass.getModifierList()));
+                        classObjectDescriptor.setTypeParameterDescriptors(new ArrayList<TypeParameterDescriptor>(0));
                         classObjectDescriptor.createTypeConstructor();
                         createPrimaryConstructorForObject(null, classObjectDescriptor);
                         mutableClassDescriptor.setClassObjectDescriptor(classObjectDescriptor);
@@ -243,6 +244,7 @@ public class TypeHierarchyResolver {
             MutableClassDescriptor descriptor = entry.getValue();
             descriptor.setModality(Modality.FINAL);
             descriptor.setVisibility(DescriptorResolver.resolveVisibilityFromModifiers(objectDeclaration.getModifierList()));
+            descriptor.setTypeParameterDescriptors(new ArrayList<TypeParameterDescriptor>(0));
             descriptor.createTypeConstructor();
         }
     }