diff --git a/internal/stream/stream_test.go b/internal/stream/stream_test.go
index 2148cc7..178f691 100644
--- a/internal/stream/stream_test.go
+++ b/internal/stream/stream_test.go
@@ -10,8 +10,10 @@ import (
 	"bytes"
 	"crypto/rand"
 	"fmt"
+	"io"
 	"testing"
 
+	"github.com/FiloSottile/age/internal/format"
 	"github.com/FiloSottile/age/internal/stream"
 	"golang.org/x/crypto/chacha20poly1305"
 )
@@ -38,7 +40,19 @@ func testRoundTrip(t *testing.T, stepSize, length int) {
 		t.Fatal(err)
 	}
 
-	w, err := stream.NewWriter(key, buf)
+	var closed bool
+	bufCloser := struct {
+		io.Writer
+		format.CloserFunc
+	}{
+		Writer: buf,
+		CloserFunc: func() error {
+			closed = true
+			return nil
+		},
+	}
+
+	w, err := stream.NewWriter(key, bufCloser)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -70,6 +84,9 @@ func testRoundTrip(t *testing.T, stepSize, length int) {
 	if err := w.Close(); err != nil {
 		t.Error("Close returned an error:", err)
 	}
+	if !closed {
+		t.Error("(*stream.Writer).Close didn't close the underlying WriteCloser")
+	}
 
 	t.Logf("buffer size: %d", buf.Len())