diff --git a/cmd/bundle/main.go b/cmd/bundle/main.go
index cfafff25..5f38e354 100644
--- a/cmd/bundle/main.go
+++ b/cmd/bundle/main.go
@@ -159,7 +159,10 @@ func main() {
 		}
 	}
 
-	code := bundle(args[0], *dstPath, *pkgName, *prefix)
+	code, err := bundle(args[0], *dstPath, *pkgName, *prefix)
+	if err != nil {
+		log.Fatal(err)
+	}
 	if *outputFile != "" {
 		err := ioutil.WriteFile(*outputFile, code, 0666)
 		if err != nil {
@@ -175,7 +178,7 @@ func main() {
 
 var ctxt = &build.Default
 
-func bundle(src, dst, dstpkg, prefix string) []byte {
+func bundle(src, dst, dstpkg, prefix string) ([]byte, error) {
 	// Load the initial package.
 	conf := loader.Config{ParserMode: parser.ParseComments, Build: ctxt}
 	conf.TypeCheckFuncBodies = func(p string) bool { return p == src }
@@ -183,7 +186,7 @@ func bundle(src, dst, dstpkg, prefix string) []byte {
 
 	lprog, err := conf.Load()
 	if err != nil {
-		log.Fatal(err)
+		return nil, err
 	}
 
 	info := lprog.Package(src)
@@ -251,7 +254,7 @@ func bundle(src, dst, dstpkg, prefix string) []byte {
 	for _, f := range info.Files {
 		for _, imp := range f.Imports {
 			if imp.Name != nil {
-				log.Fatalf("%s: renaming imports not supported",
+				return nil, fmt.Errorf("%s: renaming imports not supported",
 					lprog.Fset.Position(imp.Pos()))
 			}
 		}
@@ -326,7 +329,7 @@ func bundle(src, dst, dstpkg, prefix string) []byte {
 		log.Fatalf("formatting failed: %v", err)
 	}
 
-	return result
+	return result, nil
 }
 
 type flagFunc func(string)
diff --git a/cmd/bundle/main_test.go b/cmd/bundle/main_test.go
index b4d0810f..009fc99b 100644
--- a/cmd/bundle/main_test.go
+++ b/cmd/bundle/main_test.go
@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"io/ioutil"
+	"os"
 	"os/exec"
 	"runtime"
 	"testing"
@@ -33,17 +34,18 @@ func TestBundle(t *testing.T) {
 		},
 	})
 
-	var out bytes.Buffer
-	if err := bundle(&out, "initial", "dest", "prefix"); err != nil {
+	os.Args = os.Args[:1] // avoid e.g. -test=short in the output
+	out, err := bundle("initial", "github.com/dest", "dest", "prefix")
+	if err != nil {
 		t.Fatal(err)
 	}
-	if got, want := out.String(), load("testdata/out.golden"); got != want {
+	if got, want := string(out), load("testdata/out.golden"); got != want {
 		t.Errorf("-- got --\n%s\n-- want --\n%s\n-- diff --", got, want)
 
-		if err := ioutil.WriteFile("testdata/out.got", out.Bytes(), 0644); err != nil {
+		if err := ioutil.WriteFile("testdata/out.got", out, 0644); err != nil {
 			t.Fatal(err)
 		}
-		t.Log(diff("testdata/out.got", "testdata/out.golden"))
+		t.Log(diff("testdata/out.golden", "testdata/out.got"))
 	}
 }
 
diff --git a/cmd/bundle/testdata/out.golden b/cmd/bundle/testdata/out.golden
index 5153d3fc..2b1784e7 100644
--- a/cmd/bundle/testdata/out.golden
+++ b/cmd/bundle/testdata/out.golden
@@ -1,5 +1,5 @@
-// Code generated by golang.org/x/tools/cmd/bundle command:
-//   $ bundle initial dest prefix
+// Code generated by golang.org/x/tools/cmd/bundle.
+//   $ bundle
 
 // The package doc comment
 //