diff --git a/opcua/tools.py b/opcua/tools.py
index 889cd5fe..cc93269e 100644
--- a/opcua/tools.py
+++ b/opcua/tools.py
@@ -418,8 +418,9 @@ def application_to_strings(app):
     for (n, v) in optionals:
         if v:
             result.append((n, v))
-    for url in app.DiscoveryUrls:
-        result.append(('Discovery URL', url))
+    if app.DiscoveryUrls:
+        for url in app.DiscoveryUrls:
+            result.append(('Discovery URL', url))
     return result  # ['{}: {}'.format(n, v) for (n, v) in result]