diff --git a/container/initoverlay.go b/container/initoverlay.go
index 718b965..81b00b9 100644
--- a/container/initoverlay.go
+++ b/container/initoverlay.go
@@ -163,11 +163,10 @@ func (o *MountOverlayOp) apply(state *setupState) error {
 
 func (o *MountOverlayOp) Is(op Op) bool {
 	vo, ok := op.(*MountOverlayOp)
-	return ok &&
-		o.Target == vo.Target &&
-		slices.Equal(o.Lower, vo.Lower) &&
-		o.Upper == vo.Upper &&
-		o.Work == vo.Work
+	return ok && ((o == nil && vo == nil) || (o != nil && vo != nil &&
+		o.Target != nil && vo.Target != nil && o.Target.Is(vo.Target) &&
+		slices.EqualFunc(o.Lower, vo.Lower, func(a *Absolute, v *Absolute) bool { return a.Is(v) }) &&
+		o.Upper.Is(vo.Upper) && o.Work.Is(vo.Work)))
 }
 func (*MountOverlayOp) prefix() string { return "mounting" }
 func (o *MountOverlayOp) String() string {
diff --git a/container/initoverlay_test.go b/container/initoverlay_test.go
new file mode 100644
index 0000000..ae4cd1b
--- /dev/null
+++ b/container/initoverlay_test.go
@@ -0,0 +1,111 @@
+package container
+
+import "testing"
+
+func TestMountOverlayOp(t *testing.T) {
+	checkOpsBuilder(t, []opsBuilderTestCase{
+		{"full", new(Ops).Overlay(
+			MustAbs("/nix/store"),
+			MustAbs("/mnt-root/nix/.rw-store/upper"),
+			MustAbs("/mnt-root/nix/.rw-store/work"),
+			MustAbs("/mnt-root/nix/.ro-store"),
+		), Ops{
+			&MountOverlayOp{
+				Target: MustAbs("/nix/store"),
+				Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+				Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+				Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+			},
+		}},
+
+		{"ephemeral", new(Ops).OverlayEphemeral(MustAbs("/nix/store"), MustAbs("/mnt-root/nix/.ro-store")), Ops{
+			&MountOverlayOp{
+				Target: MustAbs("/nix/store"),
+				Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+				Upper:  MustAbs("/"),
+			},
+		}},
+
+		{"readonly", new(Ops).OverlayReadonly(MustAbs("/nix/store"), MustAbs("/mnt-root/nix/.ro-store")), Ops{
+			&MountOverlayOp{
+				Target: MustAbs("/nix/store"),
+				Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			},
+		}},
+	})
+
+	checkOpIs(t, []opIsTestCase{
+		{"zero", new(MountOverlayOp), new(MountOverlayOp), false},
+
+		{"differs target", &MountOverlayOp{
+			Target: MustAbs("/nix/store/differs"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work")}, false},
+
+		{"differs lower", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store/differs")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work")}, false},
+
+		{"differs upper", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper/differs"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work")}, false},
+
+		{"differs work", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work/differs"),
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work")}, false},
+
+		{"equals ro", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")}}, true},
+
+		{"equals", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+		}, &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work")}, true},
+	})
+
+	checkOpMeta(t, []opMetaTestCase{
+		{"nix", &MountOverlayOp{
+			Target: MustAbs("/nix/store"),
+			Lower:  []*Absolute{MustAbs("/mnt-root/nix/.ro-store")},
+			Upper:  MustAbs("/mnt-root/nix/.rw-store/upper"),
+			Work:   MustAbs("/mnt-root/nix/.rw-store/work"),
+		}, "mounting", `overlay on "/nix/store" with 1 layers`},
+	})
+}