diff --git a/src/net/smtp/smtp_test.go b/src/net/smtp/smtp_test.go
index 389eda9ad5..427ed0f7d9 100644
--- a/src/net/smtp/smtp_test.go
+++ b/src/net/smtp/smtp_test.go
@@ -1136,40 +1136,58 @@ func sendMail(hostPort string) error {
 
 // localhostCert is a PEM-encoded TLS cert generated from src/crypto/tls:
 //
-//	go run generate_cert.go --rsa-bits 1024 --host 127.0.0.1,::1,example.com \
+//	go run generate_cert.go --rsa-bits 2048 --host 127.0.0.1,::1,example.com \
 //		--ca --start-date "Jan 1 00:00:00 1970" --duration=1000000h
 var localhostCert = []byte(`
 -----BEGIN CERTIFICATE-----
-MIICFDCCAX2gAwIBAgIRAK0xjnaPuNDSreeXb+z+0u4wDQYJKoZIhvcNAQELBQAw
-EjEQMA4GA1UEChMHQWNtZSBDbzAgFw03MDAxMDEwMDAwMDBaGA8yMDg0MDEyOTE2
-MDAwMFowEjEQMA4GA1UEChMHQWNtZSBDbzCBnzANBgkqhkiG9w0BAQEFAAOBjQAw
-gYkCgYEA0nFbQQuOWsjbGtejcpWz153OlziZM4bVjJ9jYruNw5n2Ry6uYQAffhqa
-JOInCmmcVe2siJglsyH9aRh6vKiobBbIUXXUU1ABd56ebAzlt0LobLlx7pZEMy30
-LqIi9E6zmL3YvdGzpYlkFRnRrqwEtWYbGBf3znO250S56CCWH2UCAwEAAaNoMGYw
-DgYDVR0PAQH/BAQDAgKkMBMGA1UdJQQMMAoGCCsGAQUFBwMBMA8GA1UdEwEB/wQF
-MAMBAf8wLgYDVR0RBCcwJYILZXhhbXBsZS5jb22HBH8AAAGHEAAAAAAAAAAAAAAA
-AAAAAAEwDQYJKoZIhvcNAQELBQADgYEAbZtDS2dVuBYvb+MnolWnCNqvw1w5Gtgi
-NmvQQPOMgM3m+oQSCPRTNGSg25e1Qbo7bgQDv8ZTnq8FgOJ/rbkyERw2JckkHpD4
-n4qcK27WkEDBtQFlPihIM8hLIuzWoi/9wygiElTy/tVL3y7fGCvY2/k1KBthtZGF
-tN8URjVmyEo=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 -----END CERTIFICATE-----`)
 
 // localhostKey is the private key for localhostCert.
 var localhostKey = []byte(testingKey(`
 -----BEGIN RSA TESTING KEY-----
-MIICXgIBAAKBgQDScVtBC45ayNsa16NylbPXnc6XOJkzhtWMn2Niu43DmfZHLq5h
-AB9+Gpok4icKaZxV7ayImCWzIf1pGHq8qKhsFshRddRTUAF3np5sDOW3QuhsuXHu
-lkQzLfQuoiL0TrOYvdi90bOliWQVGdGurAS1ZhsYF/fOc7bnRLnoIJYfZQIDAQAB
-AoGBAMst7OgpKyFV6c3JwyI/jWqxDySL3caU+RuTTBaodKAUx2ZEmNJIlx9eudLA
-kucHvoxsM/eRxlxkhdFxdBcwU6J+zqooTnhu/FE3jhrT1lPrbhfGhyKnUrB0KKMM
-VY3IQZyiehpxaeXAwoAou6TbWoTpl9t8ImAqAMY8hlULCUqlAkEA+9+Ry5FSYK/m
-542LujIcCaIGoG1/Te6Sxr3hsPagKC2rH20rDLqXwEedSFOpSS0vpzlPAzy/6Rbb
-PHTJUhNdwwJBANXkA+TkMdbJI5do9/mn//U0LfrCR9NkcoYohxfKz8JuhgRQxzF2
-6jpo3q7CdTuuRixLWVfeJzcrAyNrVcBq87cCQFkTCtOMNC7fZnCTPUv+9q1tcJyB
-vNjJu3yvoEZeIeuzouX9TJE21/33FaeDdsXbRhQEj23cqR38qFHsF1qAYNMCQQDP
-QXLEiJoClkR2orAmqjPLVhR3t2oB3INcnEjLNSq8LHyQEfXyaFfu4U9l5+fRPL2i
-jiC0k/9L5dHUsF0XZothAkEA23ddgRs+Id/HxtojqqUT27B8MT/IGNrYsp4DvS/c
-qgkeluku4GjxRlDMBuXk94xOBEinUs+p/hwP1Alll80Tpg==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 -----END RSA TESTING KEY-----`))
 
 func testingKey(s string) string { return strings.ReplaceAll(s, "TESTING KEY", "PRIVATE KEY") }