diff --git a/js/js.tests/test/org/jetbrains/k2js/test/semantics/CastTest.java b/js/js.tests/test/org/jetbrains/k2js/test/semantics/CastTest.java
index 7dee4df742c..74cab0ed722 100644
--- a/js/js.tests/test/org/jetbrains/k2js/test/semantics/CastTest.java
+++ b/js/js.tests/test/org/jetbrains/k2js/test/semantics/CastTest.java
@@ -31,4 +31,12 @@ public final class CastTest extends AbstractExpressionTest {
     public void testCastToNotNullType() throws Exception {
         checkFooBoxIsOk();
     }
+
+    public void testSmartCastInExtensionFunction() throws Exception {
+        checkFooBoxIsOk();
+    }
+
+    public void testSmartCastInFunction() throws Exception {
+        checkFooBoxIsOk();
+    }
 }
diff --git a/js/js.translator/src/org/jetbrains/k2js/translate/utils/JsDescriptorUtils.java b/js/js.translator/src/org/jetbrains/k2js/translate/utils/JsDescriptorUtils.java
index 8d178667eb4..49b51891e79 100644
--- a/js/js.translator/src/org/jetbrains/k2js/translate/utils/JsDescriptorUtils.java
+++ b/js/js.translator/src/org/jetbrains/k2js/translate/utils/JsDescriptorUtils.java
@@ -24,8 +24,10 @@ import org.jetbrains.jet.lang.descriptors.*;
 import org.jetbrains.jet.lang.psi.JetExpression;
 import org.jetbrains.jet.lang.resolve.BindingContext;
 import org.jetbrains.jet.lang.resolve.DescriptorUtils;
+import org.jetbrains.jet.lang.resolve.calls.autocasts.AutoCastReceiver;
 import org.jetbrains.jet.lang.resolve.name.Name;
 import org.jetbrains.jet.lang.resolve.scopes.receivers.ReceiverValue;
+import org.jetbrains.jet.lang.resolve.scopes.receivers.ThisReceiver;
 import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.lang.types.expressions.OperatorConventions;
 import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
@@ -112,12 +114,20 @@ public final class JsDescriptorUtils {
     }
 
     @NotNull
-    public static DeclarationDescriptor getDeclarationDescriptorForReceiver
-            (@NotNull ReceiverValue receiverParameter) {
-        DeclarationDescriptor declarationDescriptor =
-                receiverParameter.getType().getConstructor().getDeclarationDescriptor();
-        //TODO: WHY assert?
-        assert declarationDescriptor != null;
+    public static DeclarationDescriptor getDeclarationDescriptorForReceiver(@NotNull ReceiverValue receiverParameter) {
+        DeclarationDescriptor declarationDescriptor;
+
+        if (receiverParameter instanceof ThisReceiver) {
+            declarationDescriptor = ((ThisReceiver) receiverParameter).getDeclarationDescriptor();
+        }
+        else if (receiverParameter instanceof AutoCastReceiver) {
+            AutoCastReceiver autoCastReceiver = ((AutoCastReceiver) receiverParameter);
+            declarationDescriptor = getDeclarationDescriptorForReceiver(autoCastReceiver.getOriginal());
+        }
+        else {
+            throw new UnsupportedOperationException("Unsupported receiver type: " + receiverParameter);
+        }
+
         return declarationDescriptor.getOriginal();
     }
 
diff --git a/js/js.translator/testFiles/expression/cast/cases/smartCastInExtensionFunction.kt b/js/js.translator/testFiles/expression/cast/cases/smartCastInExtensionFunction.kt
new file mode 100644
index 00000000000..d452aba6877
--- /dev/null
+++ b/js/js.translator/testFiles/expression/cast/cases/smartCastInExtensionFunction.kt
@@ -0,0 +1,59 @@
+package foo
+
+class A {
+    fun foo(a: Int) = "A.foo($a)"
+}
+
+fun Any.bar() = "Any.bar()"
+fun A.bar() = "A.bar()"
+
+fun boo(a: Any) = "boo(Any)"
+fun boo(a: A) = "boo(A)"
+
+fun assert<T>(expected: T, actual: T, caseName: String) {
+    if (expected != actual) throw Exception("Filed on $caseName, expected: $expected, actual: $actual")
+}
+
+fun Any.testInTopLevel() {
+    assert(bar(), "Any.bar()", "bar()")
+    assert(this.bar(), "Any.bar()", "this.bar()")
+    assert(boo(this), "boo(Any)", "boo(this)")
+
+    if (this is A) {
+        assert(foo(47), "A.foo(47)", "foo(47)")
+        assert(bar(), "A.bar()", "bar()")
+
+        assert(this.foo(47), "A.foo(47)", "this.foo(47)")
+        assert(this.bar(), "A.bar()", "this.bar()")
+
+        assert(boo(this), "boo(A)", "boo(this: A)")
+    }
+}
+
+class B {
+    fun Any.test() {
+        assert(bar(), "Any.bar()", "bar()")
+        assert(this.bar(), "Any.bar()", "this.bar()")
+        assert(boo(this), "boo(Any)", "boo(this)")
+
+        if (this is A) {
+            assert(foo(47), "A.foo(47)", "foo(47)")
+            assert(bar(), "A.bar()", "bar()")
+
+            assert(this.foo(47), "A.foo(47)", "this.foo(47)")
+            assert(this.bar(), "A.bar()", "this.bar()")
+
+            assert(boo(this), "boo(A)", "boo(this: A)")
+        }
+    }
+
+    fun testInClass() {
+        A().test()
+    }
+}
+
+fun box(): String {
+    A().testInTopLevel()
+    B().testInClass()
+    return "OK"
+}
diff --git a/js/js.translator/testFiles/expression/cast/cases/smartCastInFunction.kt b/js/js.translator/testFiles/expression/cast/cases/smartCastInFunction.kt
new file mode 100644
index 00000000000..94029bb71de
--- /dev/null
+++ b/js/js.translator/testFiles/expression/cast/cases/smartCastInFunction.kt
@@ -0,0 +1,49 @@
+package foo
+
+class A {
+    fun foo(a: Int) = "A.foo($a)"
+}
+
+fun Any.bar() = "Any.bar()"
+fun A.bar() = "A.bar()"
+
+fun boo(a: Any) = "boo(Any)"
+fun boo(a: A) = "boo(A)"
+
+fun assert<T>(expected: T, actual: T, caseName: String) {
+    if (expected != actual) throw Exception("Filed on $caseName, expected: $expected, actual: $actual")
+}
+
+fun testInTopLevel(a: Any) {
+    assert(a.bar(), "Any.bar()", "bar()")
+    assert(a.bar(), "Any.bar()", "this.bar()")
+    assert(boo(a), "boo(Any)", "boo(this)")
+
+    if (a is A) {
+        assert(a.foo(47), "A.foo(47)", "a.foo(47)")
+        assert(a.bar(), "A.bar()", "a.bar()")
+        assert(boo(a), "boo(A)", "boo(a: A)")
+    }
+}
+
+class B {
+    fun testInClass(a: Any) {
+        assert(a.bar(), "Any.bar()", "bar()")
+        assert(a.bar(), "Any.bar()", "this.bar()")
+        assert(boo(a), "boo(Any)", "boo(this)")
+
+        if (a is A) {
+            assert(a.foo(47), "A.foo(47)", "a.foo(47)")
+            assert(a.bar(), "A.bar()", "a.bar()")
+            assert(boo(a), "boo(A)", "boo(a: A)")
+        }
+    }
+
+}
+
+fun box(): String {
+    testInTopLevel(A())
+    B().testInClass(A())
+
+    return "OK"
+}