diff --git a/nbxmpp/tls_nb.py b/nbxmpp/tls_nb.py
index 3a6608dbe525e341d3a790e8e6f93b2d242ca0d1..657a9295721276a14ea9f373da1436ec56ca1d3c 100644
--- a/nbxmpp/tls_nb.py
+++ b/nbxmpp/tls_nb.py
@@ -333,7 +333,7 @@ class NonBlockingTLS(PlugIn):
         if not os.path.isfile(cert_path):
             return
         try:
-            f = open(cert_path, encoding='utf-8')
+            f = open(cert_path, encoding='ISO-8859-1')
             lines = f.readlines()
         except (IOError, UnicodeError) as e:
             log.warning('Unable to open certificate file %s: %s' % \