diff --git a/src/org/mozilla/javascript/ScriptableObject.java b/src/org/mozilla/javascript/ScriptableObject.java
index 8259f0746f..6b60865c7c 100644
--- a/src/org/mozilla/javascript/ScriptableObject.java
+++ b/src/org/mozilla/javascript/ScriptableObject.java
@@ -2483,6 +2483,14 @@ boolean putImpl(Object key, int index, Scriptable start, Object value, boolean i
             if (slot == null) {
                 return false;
             }
+            // If this object is not the Receiver (start) object
+            // and if the slot is a Writeable data descriptor
+            // then invoke putImpl() on the Receiver (start) object
+            if (slot.isValueSlot()
+                    && !slot.isReadOnly(isThrow)
+                    && start instanceof ScriptableObject) {
+                return ((ScriptableObject) start).putImpl(key, index, start, value, isThrow);
+            }
         } else if (!isExtensible) {
             slot = slotMap.query(key, index);
             if ((slot == null
diff --git a/src/org/mozilla/javascript/Slot.java b/src/org/mozilla/javascript/Slot.java
index ac0e445312..cc77e923b5 100644
--- a/src/org/mozilla/javascript/Slot.java
+++ b/src/org/mozilla/javascript/Slot.java
@@ -40,6 +40,24 @@ boolean isSetterSlot() {
         return false;
     }
 
+    /**
+     * Return true if this Slot has the {@link ScriptableObject#READONLY read-only} {@link
+     * #getAttributes() attribute}. Callers may wish to check if this is a {@link #isValueSlot()
+     * value slot} first.
+     *
+     * @param isThrow set to true to throw a type error instead of returning true
+     * @return true if this slot is read-only and {@code isThrow} is false
+     */
+    boolean isReadOnly(boolean isThrow) {
+        if ((attributes & ScriptableObject.READONLY) != 0) {
+            if (isThrow) {
+                throw ScriptRuntime.typeErrorById("msg.modify.readonly", name);
+            }
+            return true;
+        }
+        return false;
+    }
+
     protected Slot(Slot oldSlot) {
         name = oldSlot.name;
         indexOrHash = oldSlot.indexOrHash;
@@ -61,10 +79,7 @@ public final boolean setValue(Object value, Scriptable owner, Scriptable start)
     }
 
     public boolean setValue(Object value, Scriptable owner, Scriptable start, boolean isThrow) {
-        if ((attributes & ScriptableObject.READONLY) != 0) {
-            if (isThrow) {
-                throw ScriptRuntime.typeErrorById("msg.modify.readonly", name);
-            }
+        if (isReadOnly(isThrow)) {
             return true;
         }
         if (owner == start) {
diff --git a/testsrc/org/mozilla/javascript/tests/es6/NativeObjectTest.java b/testsrc/org/mozilla/javascript/tests/es6/NativeObjectTest.java
index c15e5425d6..40d09c9d9c 100644
--- a/testsrc/org/mozilla/javascript/tests/es6/NativeObjectTest.java
+++ b/testsrc/org/mozilla/javascript/tests/es6/NativeObjectTest.java
@@ -148,6 +148,76 @@ public void testAssignUnwritable() {
                 "error");
     }
 
+    @Test
+    public void testAssignVariousKeyTypes() {
+        evaluateAndAssert(
+                "var strKeys = Object.assign({}, {a: 1, b: 2});\n"
+                        + "var arrayKeys = Object.assign({}, ['a', 'b']);\n"
+                        + "var res = 'strKeys: ' + JSON.stringify(strKeys) + "
+                        + "'  arrayKeys:' + JSON.stringify(arrayKeys);\n"
+                        + "res",
+                "strKeys: {\"a\":1,\"b\":2}  arrayKeys:{\"0\":\"a\",\"1\":\"b\"}");
+    }
+
+    @Test
+    public void testAssignWithPrototypeStringKeys() {
+        final String script =
+                "var targetProto = { a: 1, b: 2 };\n"
+                        + "var target = Object.create(targetProto);\n"
+                        + "var source = { b: 4, c: 5 };\n"
+                        + "var assigned = Object.assign(target, source);\n"
+                        + "var res = 'targetProto: ' + JSON.stringify(targetProto) + "
+                        + "'  target: ' + JSON.stringify(target) + "
+                        + "'  assigned: ' + JSON.stringify(assigned);\n"
+                        + "res";
+
+        evaluateAndAssert(
+                script,
+                "targetProto: {\"a\":1,\"b\":2}  target: {\"b\":4,\"c\":5}  assigned: {\"b\":4,\"c\":5}");
+    }
+
+    @Test
+    public void testAssignWithPrototypeNumericKeys() {
+        final String script =
+                "var targetProto = {0: 'a', 1: 'b'};\n"
+                        + "var target = Object.create(targetProto);\n"
+                        + "var source = {1: 'c', 2: 'd'};\n"
+                        + "var assigned = Object.assign(target, source);\n"
+                        + "var res = 'targetProto: ' + JSON.stringify(targetProto) + "
+                        + "'  target: ' + JSON.stringify(target) + "
+                        + "'  assigned: ' + JSON.stringify(assigned);\n"
+                        + "res";
+
+        evaluateAndAssert(
+                script,
+                "targetProto: {\"0\":\"a\",\"1\":\"b\"}  target: {\"1\":\"c\",\"2\":\"d\"}  assigned: {\"1\":\"c\",\"2\":\"d\"}");
+    }
+
+    @Test
+    public void testAssignWithPrototypeWithGettersAndSetters() {
+        final String script =
+                "var targetProto = {"
+                        + "_a: 1, get a() { return this._a }, set a(val) { this._a = val+10 },"
+                        + " _b: 2, get b() { return this._b }, set b(val) { this._b = val+10 }"
+                        + "};\n"
+                        + "var target = Object.create(targetProto);\n"
+                        + "var source = {"
+                        + "_b: 4, get b() { return this._b * 4 }, set b(val) { this._b = val+10 },"
+                        + " _c: 5, get c() { return this._c }, set c(val) { this._c = val+10 }};\n"
+                        + "var assigned = Object.assign(target, source);\n"
+                        + "var res = 'targetProto: ' + JSON.stringify(targetProto) + "
+                        + "'  target: ' + JSON.stringify(target) + "
+                        + "'  assigned: ' + JSON.stringify(assigned) + "
+                        + "'  assigned.a: ' + assigned.a + "
+                        + "'  assigned.b: ' + assigned.b + "
+                        + "'  assigned.c: ' + assigned.c;\n"
+                        + "res";
+
+        evaluateAndAssert(
+                script,
+                "targetProto: {\"_a\":1,\"a\":1,\"_b\":2,\"b\":2}  target: {\"_b\":26,\"_c\":5,\"c\":5}  assigned: {\"_b\":26,\"_c\":5,\"c\":5}  assigned.a: 1  assigned.b: 26  assigned.c: 5");
+    }
+
     @Test
     public void testSetPrototypeOfNull() {
         evaluateAndAssert(