diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/AsmUtil.java b/compiler/backend/src/org/jetbrains/jet/codegen/AsmUtil.java
index 5ed1aa1497a..9b469c9a249 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/AsmUtil.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/AsmUtil.java
@@ -50,7 +50,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import static org.jetbrains.jet.codegen.JvmCodegenUtil.getSuperClass;
 import static org.jetbrains.jet.codegen.JvmCodegenUtil.isInterface;
 import static org.jetbrains.jet.lang.resolve.DescriptorUtils.*;
 import static org.jetbrains.jet.lang.resolve.java.AsmTypeConstants.JAVA_STRING_TYPE;
@@ -320,16 +319,6 @@ public class AsmUtil {
         return null;
     }
 
-    @NotNull
-    public static Type getTraitImplThisParameterType(@NotNull ClassDescriptor traitDescriptor, @NotNull JetTypeMapper typeMapper) {
-        JetType jetType = getSuperClass(traitDescriptor);
-        Type type = typeMapper.mapType(jetType);
-        if (type.getInternalName().equals("java/lang/Object")) {
-            return typeMapper.mapType(traitDescriptor.getDefaultType());
-        }
-        return type;
-    }
-
     private static Type stringValueOfType(Type type) {
         int sort = type.getSort();
         return sort == Type.OBJECT || sort == Type.ARRAY
diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java b/compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java
index 70db32ebf32..b82c717874e 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java
@@ -1497,27 +1497,25 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
                     @Override
                     public void doGenerateBody(@NotNull ExpressionCodegen codegen, @NotNull JvmMethodSignature signature) {
                         DeclarationDescriptor containingDeclaration = traitFun.getContainingDeclaration();
-                        if (!(containingDeclaration instanceof ClassDescriptor)) return;
-                        ClassDescriptor containingTrait = (ClassDescriptor) containingDeclaration;
-                        if (containingTrait.getKind() != ClassKind.TRAIT) return;
+                        if (!DescriptorUtils.isTrait(containingDeclaration)) return;
+                        Type traitImplType = typeMapper.mapTraitImpl((ClassDescriptor) containingDeclaration);
 
-                        Method traitMethod = typeMapper.mapSignature(traitFun.getOriginal()).getAsmMethod();
+                        Method traitMethod = typeMapper.mapSignature(traitFun.getOriginal(), OwnerKind.TRAIT_IMPL).getAsmMethod();
 
                         Type[] argTypes = signature.getAsmMethod().getArgumentTypes();
                         Type[] originalArgTypes = traitMethod.getArgumentTypes();
+                        assert originalArgTypes.length == argTypes.length + 1 :
+                                "Invalid trait implementation signature: " + signature + " vs " + traitMethod + " for " + traitFun;
 
                         InstructionAdapter iv = codegen.v;
                         iv.load(0, OBJECT_TYPE);
                         for (int i = 0, reg = 1; i < argTypes.length; i++) {
-                            StackValue.local(reg, argTypes[i]).put(originalArgTypes[i], iv);
+                            StackValue.local(reg, argTypes[i]).put(originalArgTypes[i + 1], iv);
                             //noinspection AssignmentToForLoopParameter
                             reg += argTypes[i].getSize();
                         }
 
-                        Type type = getTraitImplThisParameterType(containingTrait, typeMapper);
-                        String desc = traitMethod.getDescriptor().replace("(", "(" + type.getDescriptor());
-
-                        iv.invokestatic(typeMapper.mapTraitImpl(containingTrait).getInternalName(), traitMethod.getName(), desc);
+                        iv.invokestatic(traitImplType.getInternalName(), traitMethod.getName(), traitMethod.getDescriptor());
 
                         Type returnType = signature.getReturnType();
                         StackValue.onStack(traitMethod.getReturnType()).put(returnType, iv);
diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/JvmCodegenUtil.java b/compiler/backend/src/org/jetbrains/jet/codegen/JvmCodegenUtil.java
index 0ef0e12f128..91f34a84d66 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/JvmCodegenUtil.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/JvmCodegenUtil.java
@@ -81,16 +81,6 @@ public class JvmCodegenUtil {
         return stack.empty() ? null : stack.peek();
     }
 
-    public static JetType getSuperClass(ClassDescriptor classDescriptor) {
-        List<ClassDescriptor> superclassDescriptors = DescriptorUtils.getSuperclassDescriptors(classDescriptor);
-        for (ClassDescriptor descriptor : superclassDescriptors) {
-            if (descriptor.getKind() != ClassKind.TRAIT) {
-                return descriptor.getDefaultType();
-            }
-        }
-        return KotlinBuiltIns.getInstance().getAnyType();
-    }
-
     @Nullable
     public static FunctionDescriptor getDeclaredFunctionByRawSignature(
             @NotNull ClassDescriptor owner,
diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/state/JetTypeMapper.java b/compiler/backend/src/org/jetbrains/jet/codegen/state/JetTypeMapper.java
index 6d52e05603b..e7badc17e59 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/state/JetTypeMapper.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/state/JetTypeMapper.java
@@ -60,7 +60,8 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
-import static org.jetbrains.jet.codegen.AsmUtil.*;
+import static org.jetbrains.jet.codegen.AsmUtil.boxType;
+import static org.jetbrains.jet.codegen.AsmUtil.isStatic;
 import static org.jetbrains.jet.codegen.JvmCodegenUtil.*;
 import static org.jetbrains.jet.codegen.binding.CodegenBinding.*;
 import static org.jetbrains.jet.lang.resolve.BindingContextUtils.isVarCapturedInClosure;
@@ -661,16 +662,26 @@ public class JetTypeMapper {
             @NotNull OwnerKind kind,
             @NotNull BothSignatureWriter sw
     ) {
-        Type thisType;
+        ClassDescriptor thisType;
         if (kind == OwnerKind.TRAIT_IMPL) {
-            thisType = getTraitImplThisParameterType((ClassDescriptor) descriptor.getContainingDeclaration(), this);
+            thisType = getTraitImplThisParameterClass((ClassDescriptor) descriptor.getContainingDeclaration());
         }
         else if (isAccessor(descriptor) && descriptor.getExpectedThisObject() != null) {
-            thisType = mapClass((ClassifierDescriptor) descriptor.getContainingDeclaration());
+            thisType = (ClassDescriptor) descriptor.getContainingDeclaration();
         }
         else return;
 
-        writeParameter(sw, JvmMethodParameterKind.THIS, thisType);
+        writeParameter(sw, JvmMethodParameterKind.THIS, thisType.getDefaultType());
+    }
+
+    @NotNull
+    private static ClassDescriptor getTraitImplThisParameterClass(@NotNull ClassDescriptor traitDescriptor) {
+        for (ClassDescriptor descriptor : DescriptorUtils.getSuperclassDescriptors(traitDescriptor)) {
+            if (descriptor.getKind() != ClassKind.TRAIT) {
+                return descriptor;
+            }
+        }
+        return traitDescriptor;
     }
 
     public void writeFormalTypeParameters(@NotNull List<TypeParameterDescriptor> typeParameters, @NotNull BothSignatureWriter sw) {