diff --git a/runsc/config/config.go b/runsc/config/config.go
index ba687f7b6..bc238c324 100644
--- a/runsc/config/config.go
+++ b/runsc/config/config.go
@@ -688,7 +688,8 @@ type Overlay2 struct {
 }
 
 func defaultOverlay2() *Overlay2 {
-	return &Overlay2{}
+	// Rootfs overlay is enabled by default and backed by a file in rootfs itself.
+	return &Overlay2{RootMount: true, SubMounts: false, Medium: "self"}
 }
 
 // Set implements flag.Value.