diff --git a/src/net/textproto/header_test.go b/src/net/textproto/header_test.go
index de9405ca868..255e79a1301 100644
--- a/src/net/textproto/header_test.go
+++ b/src/net/textproto/header_test.go
@@ -4,7 +4,9 @@
 
 package textproto
 
-import "testing"
+import (
+	"testing"
+)
 
 type canonicalHeaderKeyTest struct {
 	in, out string
@@ -33,6 +35,17 @@ var canonicalHeaderKeyTests = []canonicalHeaderKeyTest{
 	{"foo bar", "foo bar"},
 }
 
+func TestNilMapSetOrAdd(t *testing.T) {
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("nil MIMEHeader caused panic: %v", r)
+		}
+	}()
+	var h MIMEHeader
+	h.Set("foo", "bar")
+	h.Add("biz", "boo")
+}
+
 func TestCanonicalMIMEHeaderKey(t *testing.T) {
 	for _, tt := range canonicalHeaderKeyTests {
 		if s := CanonicalMIMEHeaderKey(tt.in); s != tt.out {