diff --git a/src/calanonsync/ews.go b/src/calanonsync/ews.go
index a7c11ad..85428b8 100644
--- a/src/calanonsync/ews.go
+++ b/src/calanonsync/ews.go
@@ -87,7 +87,7 @@ func (er EWSRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
 			authHeaders := resp.Header["Www-Authenticate"]
 			if authHeaders != nil {
 				for _, h := range authHeaders {
-					if strings.HasPrefix(h, "BASIC") {
+					if strings.HasPrefix(h, "Basic") {
 						er.authType = authTypeBasic
 					} else if strings.HasPrefix(h, "NTLM") {
 						er.authType = authTypeNTLM