diff --git a/src/net/http/cookie.go b/src/net/http/cookie.go
index a0a4690ddc..5a67476cd4 100644
--- a/src/net/http/cookie.go
+++ b/src/net/http/cookie.go
@@ -168,7 +168,7 @@ func (c *Cookie) String() string {
 			log.Printf("net/http: invalid Cookie.Domain %q; dropping domain attribute", c.Domain)
 		}
 	}
-	if c.Expires.Unix() > 0 {
+	if validCookieExpires(c.Expires) {
 		b.WriteString("; Expires=")
 		b2 := b.Bytes()
 		b.Reset()
@@ -246,6 +246,12 @@ func validCookieDomain(v string) bool {
 	return false
 }
 
+// validCookieExpires returns whether v is a valid cookie expires-value.
+func validCookieExpires(t time.Time) bool {
+	// IETF RFC 6265 Section 5.1.1.5, the year must not be less than 1601
+	return t.Year() >= 1601
+}
+
 // isCookieDomainName returns whether s is a valid domain name or a valid
 // domain name with a leading dot '.'.  It is almost a direct copy of
 // package net's isDomainName.
diff --git a/src/net/http/cookie_test.go b/src/net/http/cookie_test.go
index 2c01040281..b3e54f8db3 100644
--- a/src/net/http/cookie_test.go
+++ b/src/net/http/cookie_test.go
@@ -56,6 +56,15 @@ var writeSetCookiesTests = []struct {
 		&Cookie{Name: "cookie-9", Value: "expiring", Expires: time.Unix(1257894000, 0)},
 		"cookie-9=expiring; Expires=Tue, 10 Nov 2009 23:00:00 GMT",
 	},
+	// According to IETF 6265 Section 5.1.1.5, the year cannot be less than 1601
+	{
+		&Cookie{Name: "cookie-10", Value: "expiring-1601", Expires: time.Date(1601, 1, 1, 1, 1, 1, 1, time.UTC)},
+		"cookie-10=expiring-1601; Expires=Mon, 01 Jan 1601 01:01:01 GMT",
+	},
+	{
+		&Cookie{Name: "cookie-11", Value: "invalid-expiry", Expires: time.Date(1600, 1, 1, 1, 1, 1, 1, time.UTC)},
+		"cookie-11=invalid-expiry",
+	},
 	// The "special" cookies have values containing commas or spaces which
 	// are disallowed by RFC 6265 but are common in the wild.
 	{