diff --git a/idea/src/jet/Library.jet b/idea/src/jet/Library.jet
index 0d535035baa..a1af5251d7e 100644
--- a/idea/src/jet/Library.jet
+++ b/idea/src/jet/Library.jet
@@ -40,12 +40,12 @@ fun Any?.equals(other : Any?) : Boolean// = this === other
 // Returns "null" for null
 fun Any?.toString() : String// = this === other
 
-class Iterator<out T> {
+trait class Iterator<out T> {
   fun next() : T
   abstract fun hasNext() : Boolean
 }
 
-class Iterable<out T> {
+trait class Iterable<out T> {
   fun iterator() : Iterator<T>
 }
 
@@ -56,11 +56,11 @@ class Array<T>(val size : Int) {
   fun iterator() : Iterator<T>
 }
 
-virtual class Comparable<in T> {
+trait class Comparable<in T> {
   fun compareTo(other : T) : Int
 }
 
-virtual class Hashable {
+trait class Hashable {
   fun hashCode() : Int
   fun equals(other : Any?) : Boolean
 }
@@ -92,7 +92,7 @@ class String() : Comparable<String> {
   fun trim(): String
 }
 
-class Range<in T : Comparable<T>> {
+trait class Range<in T : Comparable<T>> {
   fun contains(item : T) : Boolean
 }
 
diff --git a/idea/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java b/idea/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
index f746751f90c..7dab8fd1340 100644
--- a/idea/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
+++ b/idea/src/org/jetbrains/jet/lang/resolve/TopDownAnalyzer.java
@@ -606,21 +606,26 @@ public class TopDownAnalyzer {
                 : getInnerScopeForConstructor(primaryConstructor, descriptor.getScopeForMemberResolution(), true);
         final JetTypeInferrer.Services typeInferrer = semanticServices.getTypeInferrerServices(traceForConstructors, JetFlowInformationProvider.NONE); // TODO : flow
 
+        final Map<JetTypeReference, JetType> supertypes = Maps.newLinkedHashMap();
         JetVisitorVoid visitor = new JetVisitorVoid() {
-            private boolean superclassAppeared = false;
-            
+            private void recordSupertype(JetTypeReference typeReference, JetType supertype) {
+                if (supertype == null) return;
+                supertypes.put(typeReference, supertype);
+            }
+
             @Override
             public void visitDelegationByExpressionSpecifier(JetDelegatorByExpressionSpecifier specifier) {
                 if (descriptor.getClassModifiers().isTrait()) {
                     trace.getErrorHandler().genericError(specifier.getNode(), "Traits can not use delegation");
                 }
+                JetType supertype = trace.getBindingContext().get(BindingContext.TYPE, specifier.getTypeReference());
+                recordSupertype(specifier.getTypeReference(), supertype);
                 JetExpression delegateExpression = specifier.getDelegateExpression();
                 if (delegateExpression != null) {
                     JetScope scope = scopeForConstructor == null
                                      ? descriptor.getScopeForMemberResolution()
                                      : scopeForConstructor;
                     JetType type = typeInferrer.getType(scope, delegateExpression, NO_EXPECTED_TYPE);
-                    JetType supertype = trace.getBindingContext().get(BindingContext.TYPE, specifier.getTypeReference());
                     if (type != null && supertype != null && !semanticServices.getTypeChecker().isSubtypeOf(type, supertype)) {
                         trace.getErrorHandler().typeMismatch(delegateExpression, supertype, type);
                     }
@@ -629,27 +634,32 @@ public class TopDownAnalyzer {
 
             @Override
             public void visitDelegationToSuperCallSpecifier(JetDelegatorToSuperCall call) {
-                if (descriptor.getClassModifiers().isTrait()) {
-                    JetValueArgumentList valueArgumentList = call.getValueArgumentList();
-                    ASTNode node = valueArgumentList == null ? call.getNode() : valueArgumentList.getNode();
+                JetValueArgumentList valueArgumentList = call.getValueArgumentList();
+                ASTNode node = valueArgumentList == null ? call.getNode() : valueArgumentList.getNode();
+                if (descriptor.isTrait()) {
                     trace.getErrorHandler().genericError(node, "Traits can not initialize supertypes");
                 }
                 JetTypeReference typeReference = call.getTypeReference();
                 if (typeReference != null) {
                     if (descriptor.getUnsubstitutedPrimaryConstructor() != null) {
-                        JetType type = typeInferrer.getCallResolver().resolveCall(trace, scopeForConstructor, null, call, NO_EXPECTED_TYPE);
-                        if (type != null) {
-                            DeclarationDescriptor declarationDescriptor = type.getConstructor().getDeclarationDescriptor();
-                            if (declarationDescriptor instanceof ClassDescriptor) {
-                                ClassDescriptor classDescriptor = (ClassDescriptor) declarationDescriptor;
-                                if (classDescriptor.getClassModifiers().isTrait()) {
-                                    trace.getErrorHandler().genericError(call.getValueArgumentList().getNode(), "A trait may not have a constructor");
+                        JetType supertype = typeInferrer.getCallResolver().resolveCall(trace, scopeForConstructor, null, call, NO_EXPECTED_TYPE);
+                        if (supertype != null) {
+                            recordSupertype(typeReference, supertype);
+                            ClassDescriptor classDescriptor = TypeUtils.getClassDescriptor(supertype);
+                            if (classDescriptor != null) {
+                                if (classDescriptor.isTrait()) {
+                                    trace.getErrorHandler().genericError(node, "A trait may not have a constructor");
                                 }
                             }
                         }
+                        else {
+                            recordSupertype(typeReference, trace.getBindingContext().get(BindingContext.TYPE, typeReference));
+                        }
                     }
-                    else {
-                        JetValueArgumentList valueArgumentList = call.getValueArgumentList();
+                    else if (!descriptor.isTrait()) {
+                        JetType supertype = trace.getBindingContext().get(BindingContext.TYPE, typeReference);
+                        recordSupertype(typeReference, supertype);                        
+
                         assert valueArgumentList != null;
                         trace.getErrorHandler().genericError(valueArgumentList.getNode(),
                                                              "Class " + JetPsiUtil.safeName(jetClass.getName()) + " must have a constructor in order to be able to initialize supertypes");
@@ -659,31 +669,18 @@ public class TopDownAnalyzer {
 
             @Override
             public void visitDelegationToSuperClassSpecifier(JetDelegatorToSuperClass specifier) {
-                JetType supertype = trace.getBindingContext().get(BindingContext.TYPE, specifier.getTypeReference());
+                JetTypeReference typeReference = specifier.getTypeReference();
+                JetType supertype = trace.getBindingContext().get(BindingContext.TYPE, typeReference);
+                recordSupertype(typeReference, supertype);
                 if (supertype != null) {
-                    DeclarationDescriptor declarationDescriptor = supertype.getConstructor().getDeclarationDescriptor();
-                    if (declarationDescriptor instanceof ClassDescriptor) {
-                        ClassDescriptor classDescriptor = (ClassDescriptor) declarationDescriptor;
-                        if (!descriptor.getClassModifiers().isTrait()) {
-                            if (classDescriptor.hasConstructors() && !ErrorUtils.isError(classDescriptor.getTypeConstructor()) && !classDescriptor.getClassModifiers().isTrait()) {
+                    ClassDescriptor classDescriptor = TypeUtils.getClassDescriptor(supertype);
+                    if (classDescriptor != null) {
+                        if (!descriptor.isTrait()) {
+                            if (classDescriptor.hasConstructors() && !ErrorUtils.isError(classDescriptor.getTypeConstructor()) && !classDescriptor.isTrait()) {
                                 trace.getErrorHandler().genericError(specifier.getNode(), "This type has a constructor, and thus must be initialized here");
                             }
                         }
-                        else {
-                            if (!classDescriptor.getClassModifiers().isTrait()) {
-                                if (superclassAppeared) {
-                                    trace.getErrorHandler().genericError(specifier.getNode(), "A trait may extend only one class");
-                                }
-                                else {
-                                    superclassAppeared = true;
-                                }
-                            }
-                        }
                     }
-                    else {
-                        trace.getErrorHandler().genericError(specifier.getNode(), "Only classes may serve as supertypes");
-                    }
-
                 }
             }
 
@@ -697,9 +694,52 @@ public class TopDownAnalyzer {
                 throw new UnsupportedOperationException(element.getText() + " : " + element);
             }
         };
+        
         for (JetDelegationSpecifier delegationSpecifier : jetClass.getDelegationSpecifiers()) {
             delegationSpecifier.accept(visitor);
         }
+
+
+        Set<TypeConstructor> parentEnum = Collections.emptySet();
+        if (jetClass instanceof JetEnumEntry) {
+            parentEnum = Collections.singleton(((ClassDescriptor) descriptor.getContainingDeclaration().getContainingDeclaration()).getTypeConstructor());
+        }
+
+        checkSupertypeList(descriptor, supertypes, parentEnum);
+    }
+
+    // allowedFinalSupertypes typically contains a enum type of which supertypeOwner is an entry
+    private void checkSupertypeList(@NotNull MutableClassDescriptor supertypeOwner, @NotNull Map<JetTypeReference, JetType> supertypes, Set<TypeConstructor> allowedFinalSupertypes) {
+        Set<TypeConstructor> typeConstructors = Sets.newHashSet();
+        boolean classAppeared = false;
+        for (Map.Entry<JetTypeReference, JetType> entry : supertypes.entrySet()) {
+            JetTypeReference typeReference = entry.getKey();
+            JetType supertype = entry.getValue();
+
+            ClassDescriptor classDescriptor = TypeUtils.getClassDescriptor(supertype);
+            if (classDescriptor != null) {
+                if (!classDescriptor.isTrait()) {
+                    if (classAppeared) {
+                        trace.getErrorHandler().genericError(typeReference.getNode(), "Only one class may appear in a supertype list");
+                    }
+                    else {
+                        classAppeared = true;
+                    }
+                }
+            }
+            else {
+                trace.getErrorHandler().genericError(typeReference.getNode(), "Only classes and traits may serve as supertypes");
+            }
+
+            TypeConstructor constructor = supertype.getConstructor();
+            if (!typeConstructors.add(constructor)) {
+                trace.getErrorHandler().genericError(typeReference.getNode(), "A supertype appears twice");
+            }
+
+            if (constructor.isSealed() && !allowedFinalSupertypes.contains(constructor)) {
+                trace.getErrorHandler().genericError(typeReference.getNode(), "This type is final, so it cannot be inherited from");
+            }
+        }
     }
 
     private void resolveClassAnnotations() {
diff --git a/idea/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java b/idea/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
index 28ed2b1f94d..98bca6a932a 100644
--- a/idea/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
+++ b/idea/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
@@ -253,7 +253,6 @@ public class CallResolver {
         }
         if (traceForFirstNonemptyCandidateSet != null) {
             traceForFirstNonemptyCandidateSet.commit();
-            assert resultForFirstNonemptyCandidateSet != null;
             if (resultForFirstNonemptyCandidateSet.singleDescriptor()) {
                 return resultForFirstNonemptyCandidateSet.getDescriptor();
             }
diff --git a/idea/src/org/jetbrains/jet/lang/types/TypeUtils.java b/idea/src/org/jetbrains/jet/lang/types/TypeUtils.java
index 75ed47acf37..34f32ea9203 100644
--- a/idea/src/org/jetbrains/jet/lang/types/TypeUtils.java
+++ b/idea/src/org/jetbrains/jet/lang/types/TypeUtils.java
@@ -321,6 +321,15 @@ public class TypeUtils {
         return declarationDescriptor1.getOriginal().equals(declarationDescriptor2.getOriginal());
     }
 
+    @Nullable
+    public static ClassDescriptor getClassDescriptor(@NotNull JetType type) {
+        DeclarationDescriptor declarationDescriptor = type.getConstructor().getDeclarationDescriptor();
+        if (declarationDescriptor instanceof ClassDescriptor) {
+            return (ClassDescriptor) declarationDescriptor;
+        }
+        return null;
+    }
+
     public static boolean hasUnsubstitutedTypeParameters(JetType type) {
         if(type.getConstructor().getDeclarationDescriptor() instanceof TypeParameterDescriptor)
             return true;
diff --git a/idea/testData/checker/Builders.jet b/idea/testData/checker/Builders.jet
index bc1d5d0bc5d..1d26cbbc8b2 100644
--- a/idea/testData/checker/Builders.jet
+++ b/idea/testData/checker/Builders.jet
@@ -49,7 +49,7 @@ namespace html {
 
   class Title() : TagWithText("title")
 
-  class BodyTag(name : String) : TagWithText(name) {
+  abstract class BodyTag(name : String) : TagWithText(name) {
   }
 
   class Body() : BodyTag("body") {
diff --git a/idea/testData/checker/Constructors.jet b/idea/testData/checker/Constructors.jet
index 1e964eac399..70d1ce5a88a 100644
--- a/idea/testData/checker/Constructors.jet
+++ b/idea/testData/checker/Constructors.jet
@@ -1,9 +1,9 @@
 
-class NoC
+open class NoC
 class NoC1 : NoC
 
 class WithC0() : NoC<error>()</error>
-class WithC1() : NoC
+open class WithC1() : NoC
 class NoC2 : <error>WithC1</error>
 class NoC3 : WithC1<error>()</error>
 class WithC2() : <error>WithC1</error>
diff --git a/idea/testData/checker/MultipleBounds.jet b/idea/testData/checker/MultipleBounds.jet
index e7489eabe0a..3caff264ca5 100644
--- a/idea/testData/checker/MultipleBounds.jet
+++ b/idea/testData/checker/MultipleBounds.jet
@@ -4,14 +4,14 @@ open class A() {
   fun foo() : Int = 1
 }
 
-open class B() {
+trait class B {
   fun bar() : Double = 1.0;
 }
 
-class C() : A(), B()
+class C() : A(), B
 
 class D() {
-  class object : A(), B () {}
+  class object : A(), B {}
 }
 
 class Test1<T : A>()
@@ -61,7 +61,7 @@ fun <T : A> test2(t : T)
 }
 
 val t1 = test2<<error>A</error>>(A())
-val t2 = test2<<error>B</error>>(B())
+val t2 = test2<<error>B</error>>(C())
 val t3 = test2<C>(C())
 
 class Test<<error>T</error>>
diff --git a/idea/testData/checker/Objects.jet b/idea/testData/checker/Objects.jet
index 7bf4d985c94..512fa6a0485 100644
--- a/idea/testData/checker/Objects.jet
+++ b/idea/testData/checker/Objects.jet
@@ -1,5 +1,5 @@
 namespace toplevelObjectDeclarations {
-  class Foo(y : Int) {
+  open class Foo(y : Int) {
     virtual fun foo() : Int = 1
   }
 
@@ -63,7 +63,7 @@ namespace localObjects {
     val x : Int = 0
   }
 
-  class Foo {
+  open class Foo {
     fun foo() : Int = 1
   }
 
diff --git a/idea/testData/checker/PrimaryConstructors.jet b/idea/testData/checker/PrimaryConstructors.jet
index d0a4707c60b..2ea2ef34ab9 100644
--- a/idea/testData/checker/PrimaryConstructors.jet
+++ b/idea/testData/checker/PrimaryConstructors.jet
@@ -2,7 +2,7 @@ class <error>X</error> {
   val <error>x</error> : Int
 }
 
-class Y() {
+open class Y() {
   val x : Int = 2
 }
 
diff --git a/idea/testData/checker/SupertypeListChecks.jet b/idea/testData/checker/SupertypeListChecks.jet
new file mode 100644
index 00000000000..a2dcbe1e40f
--- /dev/null
+++ b/idea/testData/checker/SupertypeListChecks.jet
@@ -0,0 +1,51 @@
+// KT-286 Check supertype lists
+
+/*
+In a supertype list:
+ Same type should not be mentioned twice
+ Same type should not be indirectly mentioned with incoherent type arguments
+ Every trait's required dependencies should be satisfied
+ No final types should appear
+ Only one class is allowed
+*/
+
+class C1()
+
+open class OC1()
+
+open class C2 {}
+
+open class C3 {}
+
+trait class T1 {}
+
+trait class T2<T> {}
+
+trait class Test<error>()</error> {
+    <error>this</error>(x : Int) {}
+}
+
+trait class Test1 : C2<error>()</error> {}
+
+trait class Test2 : C2 {}
+
+trait class Test3 : C2, <error>C3</error> {}
+
+trait class Test4 : T1 {}
+
+trait class Test5 : T1, <error>T1</error> {}
+
+trait class Test6 : <error>C1</error> {}
+
+class CTest1() : OC1() {}
+
+class CTest2 : C2 {}
+
+class CTest3 : C2, <error>C3</error> {}
+
+class CTest4 : T1 {}
+
+class CTest5 : T1, <error>T1</error> {}
+
+class CTest6 : <error>C1</error> {}
+
diff --git a/idea/testData/checker/TraitSupertypeList.jet b/idea/testData/checker/TraitSupertypeList.jet
index 1648e44d332..3aa451d6557 100644
--- a/idea/testData/checker/TraitSupertypeList.jet
+++ b/idea/testData/checker/TraitSupertypeList.jet
@@ -1,11 +1,11 @@
-class bar()
+open class bar()
 
-trait open class Foo<error>()</error> : bar<error>()</error>, bar, <error>bar</error> {
+trait open class Foo<error>()</error> : bar<error>()</error>, <error>bar</error>, <error>bar</error> {
     <error>this</error>(x : Int) {}
 }
 
 trait open class Foo2 : bar, Foo {
 }
 
-open class Foo1() : bar(), <error>bar</error>, Foo, Foo<error>()</error> {}
+open class Foo1() : bar(), <error>bar</error>, Foo, <error>Foo</error><error>()</error> {}
 open class Foo12 : bar<error>()</error>, <error>bar</error> {}
\ No newline at end of file
diff --git a/idea/testData/checker/infos/Autocasts.jet b/idea/testData/checker/infos/Autocasts.jet
index 4a201ea3397..7cf18aadd48 100644
--- a/idea/testData/checker/infos/Autocasts.jet
+++ b/idea/testData/checker/infos/Autocasts.jet
@@ -1,4 +1,4 @@
-class A() {
+<info>open</info> class A() {
   fun foo() {}
 }
 
diff --git a/idea/testData/checker/regression/Jet11.jet b/idea/testData/checker/regression/Jet11.jet
index d78aa91a35d..e2e2a110a52 100644
--- a/idea/testData/checker/regression/Jet11.jet
+++ b/idea/testData/checker/regression/Jet11.jet
@@ -1,4 +1,4 @@
 // JET-11 Redeclaration & Forward reference for classes cause an exception
-class <error>NoC</error>
+open class <error>NoC</error>
 class NoC1 : NoC
-class <error>NoC</error>
+open class <error>NoC</error>
diff --git a/idea/testData/codegen/bridge.jet b/idea/testData/codegen/bridge.jet
index 22f30c592e1..421e675e7e7 100644
--- a/idea/testData/codegen/bridge.jet
+++ b/idea/testData/codegen/bridge.jet
@@ -1,6 +1,6 @@
 import java.lang.Integer
 
-class C {
+open class C {
  fun f(): Any = "C f"
 }
 
diff --git a/idea/testData/codegen/classes/diamondInheritance.jet b/idea/testData/codegen/classes/diamondInheritance.jet
index aefec63bfda..5f4d1c3f29a 100644
--- a/idea/testData/codegen/classes/diamondInheritance.jet
+++ b/idea/testData/codegen/classes/diamondInheritance.jet
@@ -1,11 +1,13 @@
-class Base() {
+// Changed when traits were introduced. May not make sense any more
+
+open class Base() {
     public var v : Int = 0
 }
 
-class Left() : Base() {}
-class Right() : Base() {}
+open class Left() : Base() {}
+trait class Right : Base {}
 
-class D() : Left(), Right()
+class D() : Left(), Right
 
 fun vl(l : Left) : Int = l.v
 fun vr(r : Right) : Int = r.v
diff --git a/idea/testData/codegen/classes/funDelegation.jet b/idea/testData/codegen/classes/funDelegation.jet
index f56f9d0d29b..25f2acc796d 100644
--- a/idea/testData/codegen/classes/funDelegation.jet
+++ b/idea/testData/codegen/classes/funDelegation.jet
@@ -1,8 +1,8 @@
-class Base() {
+open class Base() {
     fun n(n : Int) : Int = n + 1
 }
 
-class Abstract {}
+trait class Abstract {}
 
 class Derived1() : Base(), Abstract {}
 class Derived2() : Abstract, Base() {}
diff --git a/idea/testData/codegen/classes/inheritance.jet b/idea/testData/codegen/classes/inheritance.jet
index 54445e1f860..164971fe30f 100644
--- a/idea/testData/codegen/classes/inheritance.jet
+++ b/idea/testData/codegen/classes/inheritance.jet
@@ -1,9 +1,17 @@
-class X(val x : Int) {}
-class Y(val y : Int) {}
+// Changed when traits were introduced. May not make sense any more
 
-class Point(x : Int, y : Int) : X(x) , Y(y) {}
+open class X(val x : Int) {}
+trait class Y {
+    abstract val y : Int
+}
 
-class Abstract {}
+class YImpl(val y : Int) : Y {}
+
+class Point(x : Int, yy : Int) : X(x) , Y {
+    override val y : Int = yy
+}
+
+trait class Abstract {}
 
 class P1(x : Int, yy : Y) : Abstract, X(x), Y by yy {}
 class P2(x : Int, yy : Y) : X(x), Abstract, Y by yy {}
@@ -12,12 +20,12 @@ class P4(x : Int, yy : Y) : Y by yy, Abstract, X(x) {}
 
 fun box() : String {
     if (X(239).x != 239) return "FAIL #1"
-    if (Y(239).y != 239) return "FAIL #2"
+    if (YImpl(239).y != 239) return "FAIL #2"
 
     val p = Point(240, -1)
     if (p.x + p.y != 239) return "FAIL #3"
 
-    val y = Y(-1)
+    val y = YImpl(-1)
     val p1 = P1(240, y)
     if (p1.x + p1.y != 239) return "FAIL #4"
     val p2 = P2(240, y)
diff --git a/idea/testData/codegen/classes/inheritedInnerClass.jet b/idea/testData/codegen/classes/inheritedInnerClass.jet
index 54a7b4bb78c..4717bea55a8 100644
--- a/idea/testData/codegen/classes/inheritedInnerClass.jet
+++ b/idea/testData/codegen/classes/inheritedInnerClass.jet
@@ -1,5 +1,5 @@
 class Outer() {
-  class InnerBase() {
+  open class InnerBase() {
   }
 
   class InnerDerived(): InnerBase() {
diff --git a/idea/testData/codegen/classes/inheritedMethod.jet b/idea/testData/codegen/classes/inheritedMethod.jet
index 1005cd31be7..597910dc7b4 100644
--- a/idea/testData/codegen/classes/inheritedMethod.jet
+++ b/idea/testData/codegen/classes/inheritedMethod.jet
@@ -1,4 +1,4 @@
-class Foo {
+open class Foo {
   fun xyzzy(): String = "xyzzy"
 }
 
diff --git a/idea/testData/codegen/classes/propertyDelegation.jet b/idea/testData/codegen/classes/propertyDelegation.jet
index af33786e627..3f9a5646b91 100644
--- a/idea/testData/codegen/classes/propertyDelegation.jet
+++ b/idea/testData/codegen/classes/propertyDelegation.jet
@@ -1,4 +1,4 @@
-class Base() {
+open class Base() {
     public val plain = 239
     public val read : Int
       get() = 239
@@ -10,7 +10,7 @@ class Base() {
       }
 }
 
-class Abstract {}
+trait class Abstract {}
 
 class Derived1() : Base(), Abstract {}
 class Derived2() : Abstract, Base() {}
diff --git a/idea/testData/codegen/classes/propertyInInitializer.jet b/idea/testData/codegen/classes/propertyInInitializer.jet
index 824da2313aa..ed507f6278f 100644
--- a/idea/testData/codegen/classes/propertyInInitializer.jet
+++ b/idea/testData/codegen/classes/propertyInInitializer.jet
@@ -1,7 +1,7 @@
 class Outer() {
   public val s = "xyzzy"
 
-  class InnerBase(public val name: String) {
+  open class InnerBase(public val name: String) {
   }
 
   class InnerDerived(): InnerBase(s) {
diff --git a/idea/testData/codegen/classes/rightHandOverride.jet b/idea/testData/codegen/classes/rightHandOverride.jet
index 66c47d7c1cc..eda09d25be6 100644
--- a/idea/testData/codegen/classes/rightHandOverride.jet
+++ b/idea/testData/codegen/classes/rightHandOverride.jet
@@ -1,9 +1,11 @@
-class Left() {}
-class Right() {
+// Changed when traits were introduced. May not make sense any more
+
+trait class Left {}
+open class Right() {
     virtual fun f() = 42
 }
 
-class D() : Left(), Right() {
+class D() : Left, Right() {
     override fun f() = 239
 }