diff --git a/builder.go b/builder.go
index ab07233..420370b 100644
--- a/builder.go
+++ b/builder.go
@@ -124,6 +124,10 @@
 func (builder *Builder) Commit(container *Container, repository, tag, comment, author string, config *Config) (*Image, error) {
 	// FIXME: freeze the container before copying it to avoid data corruption?
 	// FIXME: this shouldn't be in commands.
+	if err := container.EnsureMounted(); err != nil {
+		return nil, err
+	}
+
 	rwTar, err := container.ExportRw()
 	if err != nil {
 		return nil, err
diff --git a/server_test.go b/server_test.go
index b6b21cc..57e2376 100644
--- a/server_test.go
+++ b/server_test.go
@@ -91,6 +91,27 @@
 
 }
 
+func TestCommit(t *testing.T) {
+	runtime := mkRuntime(t)
+	defer nuke(runtime)
+
+	srv := &Server{runtime: runtime}
+
+	config, _, _, err := ParseRun([]string{GetTestImage(runtime).ID, "/bin/cat"}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	id, err := srv.ContainerCreate(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := srv.ContainerCommit(id, "testrepo", "testtag", "", "", config); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestCreateStartRestartStopStartKillRm(t *testing.T) {
 	runtime := mkRuntime(t)
 	defer nuke(runtime)