diff --git a/state/inmem.go b/state/inmem.go
index ff8daab8fa..a930f78c79 100644
--- a/state/inmem.go
+++ b/state/inmem.go
@@ -26,3 +26,11 @@ func (s *InmemState) WriteState(state *terraform.State) error {
 func (s *InmemState) PersistState() error {
 	return nil
 }
+
+func (s *InmemState) Lock(*LockInfo) (string, error) {
+	return "", nil
+}
+
+func (s *InmemState) Unlock(string) error {
+	return nil
+}
diff --git a/state/state.go b/state/state.go
index 9491958a39..39f81c9d1a 100644
--- a/state/state.go
+++ b/state/state.go
@@ -28,6 +28,7 @@ type State interface {
 	StateWriter
 	StateRefresher
 	StatePersister
+	Locker
 }
 
 // StateReader is the interface for things that can return a state. Retrieving