diff --git a/acme/autocert/autocert.go b/acme/autocert/autocert.go
index a50d9bf..e562609 100644
--- a/acme/autocert/autocert.go
+++ b/acme/autocert/autocert.go
@@ -32,6 +32,7 @@
 	"time"
 
 	"golang.org/x/crypto/acme"
+	"golang.org/x/net/idna"
 )
 
 // createCertRetryAfter is how much time to wait before removing a failed state
@@ -62,10 +63,16 @@
 // HostWhitelist returns a policy where only the specified host names are allowed.
 // Only exact matches are currently supported. Subdomains, regexp or wildcard
 // will not match.
+//
+// Note that all hosts will be converted to Punycode via idna.Lookup.ToASCII so that
+// Manager.GetCertificate can handle the Unicode IDN and mixedcase hosts correctly.
+// Invalid hosts will be silently ignored.
 func HostWhitelist(hosts ...string) HostPolicy {
 	whitelist := make(map[string]bool, len(hosts))
 	for _, h := range hosts {
-		whitelist[h] = true
+		if h, err := idna.Lookup.ToASCII(h); err == nil {
+			whitelist[h] = true
+		}
 	}
 	return func(_ context.Context, host string) error {
 		if !whitelist[host] {
@@ -243,7 +250,17 @@
 	if !strings.Contains(strings.Trim(name, "."), ".") {
 		return nil, errors.New("acme/autocert: server name component count invalid")
 	}
-	if strings.ContainsAny(name, `+/\`) {
+
+	// Note that this conversion is necessary because some server names in the handshakes
+	// started by some clients (such as cURL) are not converted to Punycode, which will
+	// prevent us from obtaining certificates for them. In addition, we should also treat
+	// example.com and EXAMPLE.COM as equivalent and return the same certificate for them.
+	// Fortunately, this conversion also helped us deal with this kind of mixedcase problems.
+	//
+	// Due to the "σςΣ" problem (see https://unicode.org/faq/idn.html#22), we can't use
+	// idna.Punycode.ToASCII (or just idna.ToASCII) here.
+	name, err := idna.Lookup.ToASCII(name)
+	if err != nil {
 		return nil, errors.New("acme/autocert: server name contains invalid character")
 	}
 
diff --git a/acme/autocert/autocert_test.go b/acme/autocert/autocert_test.go
index 95e12e1..91f47e5 100644
--- a/acme/autocert/autocert_test.go
+++ b/acme/autocert/autocert_test.go
@@ -209,6 +209,28 @@
 	testGetCertificate(t, man, "example.org", hello)
 }
 
+func TestGetCertificate_unicodeIDN(t *testing.T) {
+	man := &Manager{Prompt: AcceptTOS}
+	defer man.stopRenew()
+
+	hello := clientHelloInfo("σσσ.com", true)
+	testGetCertificate(t, man, "xn--4xaaa.com", hello)
+
+	hello = clientHelloInfo("σςΣ.com", true)
+	testGetCertificate(t, man, "xn--4xaaa.com", hello)
+}
+
+func TestGetCertificate_mixedcase(t *testing.T) {
+	man := &Manager{Prompt: AcceptTOS}
+	defer man.stopRenew()
+
+	hello := clientHelloInfo("example.org", true)
+	testGetCertificate(t, man, "example.org", hello)
+
+	hello = clientHelloInfo("EXAMPLE.ORG", true)
+	testGetCertificate(t, man, "example.org", hello)
+}
+
 func TestGetCertificate_ForceRSA(t *testing.T) {
 	man := &Manager{
 		Prompt:   AcceptTOS,
@@ -906,13 +928,14 @@
 }
 
 func TestHostWhitelist(t *testing.T) {
-	policy := HostWhitelist("example.com", "example.org", "*.example.net")
+	policy := HostWhitelist("example.com", "EXAMPLE.ORG", "*.example.net", "σςΣ.com")
 	tt := []struct {
 		host  string
 		allow bool
 	}{
 		{"example.com", true},
 		{"example.org", true},
+		{"xn--4xaaa.com", true},
 		{"one.example.com", false},
 		{"two.example.org", false},
 		{"three.example.net", false},
diff --git a/go.mod b/go.mod
index d2b06ca..c4af3ec 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,6 @@
 module golang.org/x/crypto
 
-require golang.org/x/sys v0.0.0-20190403152447-81d4e9dc473e
+require (
+	golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3
+	golang.org/x/sys v0.0.0-20190412213103-97732733099d
+)
diff --git a/go.sum b/go.sum
index be20559..44da498 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,8 @@
-golang.org/x/sys v0.0.0-20190403152447-81d4e9dc473e h1:nFYrTHrdrAOpShe27kaFHjsqYSEQ0KWqdWLu3xuZJts=
-golang.org/x/sys v0.0.0-20190403152447-81d4e9dc473e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 h1:0GoQqolDA55aaLxZyTzK/Y2ePZzZTUrRacwib7cNsYQ=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=