diff --git a/certificates.go b/certificates.go
index 0c4ffdb..8f73210 100644
--- a/certificates.go
+++ b/certificates.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/tls"
@@ -12,38 +13,85 @@ import (
 	"time"
 )
 
-var fallbackCertKey, _ = rsa.GenerateKey(rand.Reader, 1024)
-var fallbackCertSpecification = &x509.Certificate{
-	Subject: pkix.Name{
-		CommonName: strings.TrimPrefix(string(MainDomainSuffix), "."),
-	},
-	SerialNumber: big.NewInt(0),
-	NotBefore: time.Now(),
-	NotAfter: time.Now().AddDate(100, 0, 0),
-}
-var fallbackCertBytes, _ = x509.CreateCertificate(
-	rand.Reader,
-	fallbackCertSpecification,
-	fallbackCertSpecification,
-	fallbackCertKey.Public(),
-	fallbackCertKey,
-)
-var fallbackCert, _ = tls.X509KeyPair(pem.EncodeToMemory(&pem.Block{
-	Bytes: fallbackCertBytes,
-	Type: "CERTIFICATE",
-}), pem.EncodeToMemory(&pem.Block{
-	Bytes: x509.MarshalPKCS1PrivateKey(fallbackCertKey),
-	Type: "RSA PRIVATE KEY",
-}))
-
 // tlsConfig contains the configuration for generating, serving and cleaning up Let's Encrypt certificates.
 var tlsConfig = &tls.Config{
 	GetCertificate: func(info *tls.ClientHelloInfo) (*tls.Certificate, error) {
 		// TODO: check DNS name & get certificate from Let's Encrypt
-		return &fallbackCert, nil
+		return FallbackCertificate(), nil
 	},
 	PreferServerCipherSuites: true,
-	// TODO: optimize cipher suites, minimum TLS version, etc.
+
+	// generated 2021-07-13, Mozilla Guideline v5.6, Go 1.14.4, intermediate configuration
+	// https://ssl-config.mozilla.org/#server=go&version=1.14.4&config=intermediate&guideline=5.6
+	MinVersion: tls.VersionTLS12,
+	CipherSuites: []uint16{
+		tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+		tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+		tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+		tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+		tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
+		tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
+	},
 }
 
-// TODO: HSTS header with includeSubdomains & preload for MainDomainSuffix and RawDomain
+// GetHSTSHeader returns a HSTS header with includeSubdomains & preload for MainDomainSuffix and RawDomain, or an empty
+// string for custom domains.
+func GetHSTSHeader(host []byte) string {
+	if bytes.HasSuffix(host, MainDomainSuffix) || bytes.Equal(host, RawDomain) {
+		return "max-age=63072000; includeSubdomains; preload"
+	} else {
+		return ""
+	}
+}
+
+var fallbackCertificate *tls.Certificate
+// FallbackCertificate generates a new self-signed TLS certificate on demand.
+func FallbackCertificate() *tls.Certificate {
+	if fallbackCertificate != nil {
+		return fallbackCertificate
+	}
+
+	fallbackSerial, err := rand.Int(rand.Reader, (&big.Int{}).Lsh(big.NewInt(1), 159))
+	if err != nil {
+		panic(err)
+	}
+
+	fallbackCertKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		panic(err)
+	}
+
+	fallbackCertSpecification := &x509.Certificate{
+		Subject: pkix.Name{
+			CommonName: strings.TrimPrefix(string(MainDomainSuffix), "."),
+		},
+		SerialNumber: fallbackSerial,
+		NotBefore: time.Now(),
+		NotAfter: time.Now().AddDate(100, 0, 0),
+	}
+
+	fallbackCertBytes, err := x509.CreateCertificate(
+		rand.Reader,
+		fallbackCertSpecification,
+		fallbackCertSpecification,
+		fallbackCertKey.Public(),
+		fallbackCertKey,
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	fallbackCert, err := tls.X509KeyPair(pem.EncodeToMemory(&pem.Block{
+		Bytes: fallbackCertBytes,
+		Type: "CERTIFICATE",
+	}), pem.EncodeToMemory(&pem.Block{
+		Bytes: x509.MarshalPKCS1PrivateKey(fallbackCertKey),
+		Type: "RSA PRIVATE KEY",
+	}))
+	if err != nil {
+		panic(err)
+	}
+
+	fallbackCertificate = &fallbackCert
+	return fallbackCertificate
+}
diff --git a/handler.go b/handler.go
index 30ef031..909725f 100644
--- a/handler.go
+++ b/handler.go
@@ -28,6 +28,11 @@ func handler(ctx *fasthttp.RequestCtx) {
 	// Enable caching, but require revalidation to reduce confusion
 	ctx.Response.Header.Set("Cache-Control", "must-revalidate")
 
+	// Add HSTS for RawDomain and MainDomainSuffix
+	if hsts := GetHSTSHeader(ctx.Host()); hsts != "" {
+		ctx.Response.Header.Set("Strict-Transport-Security", hsts)
+	}
+
 	// Block all methods not required for static pages
 	if !ctx.IsGet() && !ctx.IsHead() && !ctx.IsOptions() {
 		ctx.Response.Header.Set("Allow", "GET, HEAD, OPTIONS")
@@ -275,7 +280,11 @@ func handler(ctx *fasthttp.RequestCtx) {
 func returnErrorPage(ctx *fasthttp.RequestCtx, code int) {
 	ctx.Response.SetStatusCode(code)
 	ctx.Response.Header.SetContentType("text/html; charset=utf-8")
-	ctx.Response.SetBody(bytes.ReplaceAll(NotFoundPage, []byte("%status"), []byte(strconv.Itoa(code)+" "+fasthttp.StatusMessage(code))))
+	message := fasthttp.StatusMessage(code)
+	if code == fasthttp.StatusFailedDependency {
+		message += " - owner, repo or branch doesn't exist"
+	}
+	ctx.Response.SetBody(bytes.ReplaceAll(NotFoundPage, []byte("%status"), []byte(strconv.Itoa(code)+" "+message)))
 }
 
 // BranchExistanceCacheTimeout specifies the timeout for the default branch cache. It can be quite long.
diff --git a/main.go b/main.go
index 23ab970..cc0b43f 100644
--- a/main.go
+++ b/main.go
@@ -79,7 +79,7 @@ func main() {
 	GiteaRoot = bytes.TrimSuffix(GiteaRoot, []byte{'/'})
 
 	// Use HOST and PORT environment variables to determine listening address
-	address := fmt.Sprintf("%s:%s", envOr("HOST", "[::]"), envOr("PORT", "80"))
+	address := fmt.Sprintf("%s:%s", envOr("HOST", "[::]"), envOr("PORT", "443"))
 	fmt.Printf("Listening on https://%s\n", address)
 
 	// Enable compression by wrapping the handler() method with the compression function provided by FastHTTP