diff --git a/vapid.go b/vapid.go
index ae26cfd..e9c010f 100644
--- a/vapid.go
+++ b/vapid.go
@@ -85,8 +85,8 @@ func generateVAPIDHeaders(
 		return nil, err
 	}
 
-	// Unless subscriber is an HTTPS URL, assume an e-mail address
-	if !strings.HasPrefix(subscriber, "https:") {
+	// Unless subscriber is already a URI (https: or mailto:), assume an e-mail address.
+	if !strings.HasPrefix(subscriber, "https:") && !strings.HasPrefix(subscriber, "mailto:") {
 		subscriber = "mailto:" + subscriber
 	}
 
diff --git a/vapid_test.go b/vapid_test.go
index c665e39..4190b64 100644
--- a/vapid_test.go
+++ b/vapid_test.go
@@ -108,6 +108,58 @@ func TestVAPID(t *testing.T) {
 	}
 }
 
+func TestVAPIDSubscriberFormats(t *testing.T) {
+	s := getStandardEncodedTestSubscription()
+	vapidPrivateKey, vapidPublicKey, err := GenerateVAPIDKeys()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{"bare email", "test@test.com", "mailto:test@test.com"},
+		{"mailto URI", "mailto:test@test.com", "mailto:test@test.com"},
+		{"https URI", "https://example.com/contact", "https://example.com/contact"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			vapidHeaders, err := generateVAPIDHeaders(
+				s.Endpoint,
+				tt.input,
+				vapidPublicKey,
+				vapidPrivateKey,
+				time.Now().Add(time.Hour),
+				Vapid,
+			)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			tokenString := getTokenFromAuthorizationHeader(vapidHeaders["Authorization"], Vapid, t)
+			token, _ := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
+				b64 := base64.RawURLEncoding
+				decodedVapidPrivateKey, err := b64.DecodeString(vapidPrivateKey)
+				if err != nil {
+					return nil, err
+				}
+				return generateVAPIDHeaderKeys(decodedVapidPrivateKey).Public(), nil
+			})
+
+			claims, ok := token.Claims.(jwt.MapClaims)
+			if !ok || !token.Valid {
+				t.Fatal("invalid token")
+			}
+			if claims["sub"] != tt.expected {
+				t.Fatalf("sub: expected=%q got=%q", tt.expected, claims["sub"])
+			}
+		})
+	}
+}
+
 func TestVAPIDKeys(t *testing.T) {
 	privateKey, publicKey, err := GenerateVAPIDKeys()
 	if err != nil {
diff --git a/webpush.go b/webpush.go
index e092270..2b97f97 100644
--- a/webpush.go
+++ b/webpush.go
@@ -45,7 +45,7 @@ type Options struct {
 	AuthScheme      AuthScheme // VAPID authentication scheme, defaults to "vapid"
 	HTTPClient      HTTPClient // Will replace with *http.Client by default if not included
 	RecordSize      uint32     // Limit the record size
-	Subscriber      string     // Sub in VAPID JWT token
+	Subscriber      string     // Sub in VAPID JWT token. Accepts a "mailto:" or "https:" URI; a bare value is treated as an e-mail and prefixed with "mailto:".
 	Topic           string     // Set the Topic header to collapse a pending messages (Optional)
 	TTL             int        // Set the TTL on the endpoint POST request
 	Urgency         Urgency    // Set the Urgency header to change a message priority (Optional)