diff --git a/carddav/server.go b/carddav/server.go
index 8bb9230..5470e75 100644
--- a/carddav/server.go
+++ b/carddav/server.go
@@ -223,6 +223,10 @@ func (b *backend) propfindAddressBook(propfind *internal.Propfind, ab *AddressBo
 		addressBookHomeSetName: func(*internal.RawXMLValue) (interface{}, error) {
 			return &addressbookHomeSet{Href: "/"}, nil
 		},
+		// TODO: this should be set on all resources
+		internal.CurrentUserPrincipalName: func(*internal.RawXMLValue) (interface{}, error) {
+			return &internal.CurrentUserPrincipal{Href: "/"}, nil
+		},
 	}
 
 	if ab.MaxResourceSize > 0 {
diff --git a/client.go b/client.go
index 38e5f4a..8d1cd40 100644
--- a/client.go
+++ b/client.go
@@ -1,8 +1,8 @@
 package webdav
 
 import (
-	"encoding/xml"
 	"net/http"
+	"fmt"
 
 	"github.com/emersion/go-webdav/internal"
 )
@@ -24,18 +24,20 @@ func (c *Client) SetBasicAuth(username, password string) {
 }
 
 func (c *Client) FindCurrentUserPrincipal() (string, error) {
-	name := xml.Name{"DAV:", "current-user-principal"}
-	propfind := internal.NewPropNamePropfind(name)
+	propfind := internal.NewPropNamePropfind(internal.CurrentUserPrincipalName)
 
 	resp, err := c.c.PropfindFlat("/", propfind)
 	if err != nil {
 		return "", err
 	}
 
-	var prop currentUserPrincipal
+	var prop internal.CurrentUserPrincipal
 	if err := resp.DecodeProp(&prop); err != nil {
 		return "", err
 	}
+	if prop.Unauthenticated != nil {
+		return "", fmt.Errorf("webdav: unauthenticated")
+	}
 
 	return prop.Href, nil
 }
diff --git a/elements.go b/elements.go
deleted file mode 100644
index 04bc9c7..0000000
--- a/elements.go
+++ /dev/null
@@ -1,10 +0,0 @@
-package webdav
-
-import (
-	"encoding/xml"
-)
-
-type currentUserPrincipal struct {
-	XMLName xml.Name `xml:"DAV: current-user-principal"`
-	Href    string   `xml:"href"`
-}
diff --git a/internal/elements.go b/internal/elements.go
index f7c50bf..3b6356c 100644
--- a/internal/elements.go
+++ b/internal/elements.go
@@ -11,6 +11,17 @@ import (
 
 const Namespace = "DAV:"
 
+var (
+	ResourceTypeName     = xml.Name{"DAV:", "resourcetype"}
+	DisplayNameName      = xml.Name{"DAV:", "displayname"}
+	GetContentLengthName = xml.Name{"DAV:", "getcontentlength"}
+	GetContentTypeName   = xml.Name{"DAV:", "getcontenttype"}
+	GetLastModifiedName  = xml.Name{"DAV:", "getlastmodified"}
+	GetETagName          = xml.Name{"DAV:", "getetag"}
+
+	CurrentUserPrincipalName = xml.Name{"DAV:", "current-user-principal"}
+)
+
 type Status struct {
 	Code int
 	Text string
@@ -302,15 +313,6 @@ type GetLastModified struct {
 	LastModified Time     `xml:",chardata"`
 }
 
-var (
-	ResourceTypeName     = xml.Name{"DAV:", "resourcetype"}
-	DisplayNameName      = xml.Name{"DAV:", "displayname"}
-	GetContentLengthName = xml.Name{"DAV:", "getcontentlength"}
-	GetContentTypeName   = xml.Name{"DAV:", "getcontenttype"}
-	GetLastModifiedName  = xml.Name{"DAV:", "getlastmodified"}
-	GetETagName          = xml.Name{"DAV:", "getetag"}
-)
-
 // https://tools.ietf.org/html/rfc4918#section-14.5
 type Error struct {
 	XMLName xml.Name      `xml:"DAV: error"`
@@ -322,3 +324,10 @@ type DisplayName struct {
 	XMLName xml.Name `xml:"DAV: displayname"`
 	Name    string   `xml:",chardata"`
 }
+
+// https://tools.ietf.org/html/rfc5397#section-3
+type CurrentUserPrincipal struct {
+	XMLName         xml.Name  `xml:"DAV: current-user-principal"`
+	Href            string    `xml:"href,omitempty"`
+	Unauthenticated *struct{} `xml:"unauthenticated,omitempty"`
+}