diff --git a/src/lookup.cc b/src/lookup.cc
index 256aa02d21cf..98aab68c6d94 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -308,6 +308,11 @@ void LookupIterator::PrepareTransitionToDataProperty(
     PropertyAttributes attributes, Object::StoreFromKeyed store_mode) {
   DCHECK(receiver.is_identical_to(GetStoreTarget()));
   if (state_ == TRANSITION) return;
+
+  if (!IsElement() && name()->IsPrivate()) {
+    attributes = static_cast<PropertyAttributes>(attributes | DONT_ENUM);
+  }
+
   DCHECK(state_ != LookupIterator::ACCESSOR ||
          (GetAccessors()->IsAccessorInfo() &&
           AccessorInfo::cast(*GetAccessors())->is_special_data_property()));
@@ -442,6 +447,9 @@ void LookupIterator::TransitionToAccessorProperty(
   // handled via a trap. Adding properties to primitive values is not
   // observable.
   Handle<JSObject> receiver = GetStoreTarget();
+  if (!IsElement() && name()->IsPrivate()) {
+    attributes = static_cast<PropertyAttributes>(attributes | DONT_ENUM);
+  }
 
   if (!IsElement() && !receiver->map()->is_dictionary_map()) {
     Handle<Map> old_map(receiver->map(), isolate_);
diff --git a/src/property.h b/src/property.h
index da015794df01..233233c5d4f9 100644
--- a/src/property.h
+++ b/src/property.h
@@ -36,6 +36,7 @@ class Descriptor BASE_EMBEDDED {
 
   void Init(Handle<Name> key, Handle<Object> value, PropertyDetails details) {
     DCHECK(key->IsUniqueName());
+    DCHECK_IMPLIES(key->IsPrivate(), !details.IsEnumerable());
     key_ = key;
     value_ = value;
     details_ = details;
@@ -44,6 +45,7 @@ class Descriptor BASE_EMBEDDED {
   Descriptor(Handle<Name> key, Handle<Object> value, PropertyDetails details)
       : key_(key), value_(value), details_(details) {
     DCHECK(key->IsUniqueName());
+    DCHECK_IMPLIES(key->IsPrivate(), !details_.IsEnumerable());
   }
 
   Descriptor(Handle<Name> key, Handle<Object> value,
@@ -53,6 +55,7 @@ class Descriptor BASE_EMBEDDED {
         value_(value),
         details_(attributes, type, representation, field_index) {
     DCHECK(key->IsUniqueName());
+    DCHECK_IMPLIES(key->IsPrivate(), !details_.IsEnumerable());
   }
 
   friend class DescriptorArray;
diff --git a/test/mjsunit/harmony/private.js b/test/mjsunit/harmony/private.js
index 71b4377c57d8..cd65af1c7057 100644
--- a/test/mjsunit/harmony/private.js
+++ b/test/mjsunit/harmony/private.js
@@ -278,8 +278,8 @@ function TestKeyDescriptor(obj) {
     assertEquals(i|0, desc.value)
     assertTrue(desc.configurable)
     assertEquals(i % 2 == 0, desc.writable)
-    assertEquals(i % 2 == 0, desc.enumerable)
-    assertEquals(i % 2 == 0,
+    assertEquals(false, desc.enumerable)
+    assertEquals(false,
         Object.prototype.propertyIsEnumerable.call(obj, symbols[i]))
   }
 }