diff --git a/boom/boom.go b/boom/boom.go
index 4b08c34..099543e 100644
--- a/boom/boom.go
+++ b/boom/boom.go
@@ -135,7 +135,9 @@ func (bm *Boom) setStructKey(src interface{}, key datastore.Key) error {
 			} else {
 				vfType := vf.Type()
 				if vfType.ConvertibleTo(typeOfKey) {
-					vf.Set(reflect.ValueOf(key.ParentKey()).Convert(vfType))
+					if key.ParentKey() != nil {
+						vf.Set(reflect.ValueOf(key.ParentKey()).Convert(vfType))
+					}
 					parentSet = true
 				}
 			}
@@ -265,7 +267,7 @@ func (bm *Boom) KeyError(src interface{}) (datastore.Key, error) {
 					}
 				} else {
 					vfType := vf.Type()
-					if vfType.ConvertibleTo(typeOfKey) {
+					if !vf.IsNil() && vfType.ConvertibleTo(typeOfKey) {
 						if parent != nil {
 							return nil, fmt.Errorf("boom: Only one field may be marked parent")
 						}
diff --git a/boom/boom_test.go b/boom/boom_test.go
index 01c590d..717ab14 100644
--- a/boom/boom_test.go
+++ b/boom/boom_test.go
@@ -645,6 +645,34 @@ func TestBoom_TagParent(t *testing.T) {
 	}
 }
 
+func TestBoom_TagParentWithNilParent(t *testing.T) {
+	ctx, client, cleanUp := testutils.SetupCloudDatastore(t)
+	defer cleanUp()
+
+	ctx = context.WithValue(ctx, contextClient{}, client)
+
+	bm := FromClient(ctx, client)
+
+	type Data struct {
+		ParentKey datastore.Key `datastore:"-" boom:"parent"`
+		ID        int64         `datastore:"-" boom:"id"`
+	}
+
+	key, err := bm.Put(&Data{ParentKey: nil, ID: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if v := key.ParentKey(); v != nil {
+		t.Errorf("unexpected: %v", v)
+	}
+
+	err = bm.Get(&Data{ID: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestBoom_TagKind(t *testing.T) {
 	ctx, client, cleanUp := testutils.SetupCloudDatastore(t)
 	defer cleanUp()