diff --git a/pkg/tool/http/http.go b/pkg/tool/http/http.go
index 4c6f9e6..d7e5f33 100644
--- a/pkg/tool/http/http.go
+++ b/pkg/tool/http/http.go
@@ -99,7 +99,7 @@
 	if err != nil {
 		return nil, err
 	}
-	var h http.Header
+	h := http.Header{}
 	for iter.Next() {
 		str, err := iter.Value().String()
 		if err != nil {
diff --git a/pkg/tool/http/http_test.go b/pkg/tool/http/http_test.go
new file mode 100644
index 0000000..6de2640
--- /dev/null
+++ b/pkg/tool/http/http_test.go
@@ -0,0 +1,95 @@
+// Copyright 2020 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package http
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"cuelang.org/go/cue"
+)
+
+func TestParseHeaders(t *testing.T) {
+	req := `
+	header: {
+		"Accept-Language": "en,nl"
+	}
+	trailer: {
+		"Accept-Language": "en,nl"
+		User: "foo"
+	}
+	`
+	testCases := []struct {
+		req   string
+		field string
+		out   string
+	}{{
+		field: "header",
+		out:   "nil",
+	}, {
+		req:   req,
+		field: "non-exist",
+		out:   "nil",
+	}, {
+		req:   req,
+		field: "header",
+		out:   "Accept-Language: en,nl\r\n",
+	}, {
+		req:   req,
+		field: "trailer",
+		out:   "Accept-Language: en,nl\r\nUser: foo\r\n",
+	}, {
+		req: `
+		header: {
+			"1": 'a'
+		}
+		`,
+		field: "header",
+		out:   "header.\"1\": cannot use value 'a' (type bytes) as string",
+	}, {
+		req: `
+			header: 1
+			`,
+		field: "header",
+		out:   "header: cannot use value 1 (type int) as struct",
+	}}
+	for _, tc := range testCases {
+		t.Run("", func(t *testing.T) {
+			r := cue.Runtime{}
+			inst, err := r.Compile("http headers", tc.req)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			h, err := parseHeaders(inst.Value(), tc.field)
+
+			b := &strings.Builder{}
+			switch {
+			case err != nil:
+				fmt.Fprint(b, err)
+			case h == nil:
+				b.WriteString("nil")
+			default:
+				_ = h.Write(b)
+			}
+
+			got := b.String()
+			if got != tc.out {
+				t.Errorf("got %q; want %q", got, tc.out)
+			}
+		})
+	}
+}