diff --git a/src/crypt/certificate.vala b/src/crypt/certificate.vala
index 0930c89..d8f207b 100644
--- a/src/crypt/certificate.vala
+++ b/src/crypt/certificate.vala
@@ -147,9 +147,9 @@ namespace Mconn {
 			export_to_file(key_path, export_private_key(key));
 		}
 
-		private GnuTLS.X509.Certificate cert_from_pem(uint8[] certificate_pem) {
-			var datum = GnuTLS.Datum() { data=certificate_pem,
-										 size=certificate_pem.length };
+		private GnuTLS.X509.Certificate cert_from_pem(string certificate_pem) {
+			var datum = GnuTLS.Datum() { data=certificate_pem.data,
+										 size=certificate_pem.data.length };
 
 			var cert = GnuTLS.X509.Certificate.create();
 			var res = cert.import(ref datum, GnuTLS.X509.CertificateFormat.PEM);
@@ -164,7 +164,7 @@ namespace Mconn {
 		 * @param certificate_pem PEM encoded certificate
 		 * @return SHA1 fingerprint as bytes
 		 */
-		public uint8[] fingerprint_certificate(uint8[] certificate_pem) {
+		public uint8[] fingerprint_certificate(string certificate_pem) {
 			var cert = cert_from_pem(certificate_pem);
 
 			// TOOD: make digest configurable, for now assume it's SHA1
diff --git a/test/mconn-crypt-vala-test.vala b/test/mconn-crypt-vala-test.vala
index 4b5a863..311d4b9 100644
--- a/test/mconn-crypt-vala-test.vala
+++ b/test/mconn-crypt-vala-test.vala
@@ -107,7 +107,7 @@ sCmsSGcb9ZkEQfRNGTmFFthkcnfTU9mKh8oGc/a9r0DDgYcPSCgqERt2fgiBrt85
 -----END CERTIFICATE-----""";
 	var expected = "eb2611a447085322b206fa61d4bc5869b4a55657";
 
-	var fingerprint = Crypt.fingerprint_certificate(pem.data);
+	var fingerprint = Crypt.fingerprint_certificate(pem);
 	// SHA1
 	assert(fingerprint.length == 20);