diff --git a/daemon/errors.go b/daemon/errors.go
index 7282e4f462..803c070f12 100644
--- a/daemon/errors.go
+++ b/daemon/errors.go
@@ -59,19 +59,6 @@ func (e nameConflictError) Error() string {
 
 func (nameConflictError) Conflict() {}
 
-type containerNotModifiedError struct {
-	running bool
-}
-
-func (e containerNotModifiedError) Error() string {
-	if e.running {
-		return "Container is already started"
-	}
-	return "Container is already stopped"
-}
-
-func (e containerNotModifiedError) NotModified() {}
-
 type invalidIdentifier string
 
 func (e invalidIdentifier) Error() string {
diff --git a/daemon/start.go b/daemon/start.go
index 105362bbb3..110d9c222d 100644
--- a/daemon/start.go
+++ b/daemon/start.go
@@ -30,7 +30,7 @@ func validateState(ctr *container.Container) error {
 		// already in the desired state. It's implemented as an error
 		// to make the code calling this function terminate early (as
 		// no further processing is needed).
-		return containerNotModifiedError{running: true}
+		return errdefs.NotModified(errors.New("container is already running"))
 	}
 	if ctr.RemovalInProgress || ctr.Dead {
 		return errdefs.Conflict(errors.New("container is marked for removal and cannot be started"))
diff --git a/daemon/stop.go b/daemon/stop.go
index b5b1506d73..4d22a81945 100644
--- a/daemon/stop.go
+++ b/daemon/stop.go
@@ -26,7 +26,12 @@ func (daemon *Daemon) ContainerStop(ctx context.Context, name string, options co
 		return err
 	}
 	if !ctr.IsRunning() {
-		return containerNotModifiedError{}
+		// This is not an actual error, but produces a 304 "not modified"
+		// when returned through the API to indicates the container is
+		// already in the desired state. It's implemented as an error
+		// to make the code calling this function terminate early (as
+		// no further processing is needed).
+		return errdefs.NotModified(errors.New("container is already stopped"))
 	}
 	err = daemon.containerStop(ctx, ctr, options)
 	if err != nil {