diff --git a/avocado/core/tree.py b/avocado/core/tree.py
index 2406b39a73e4b62489fba7ca38626d00be627eee..4d2fbc817de871763420552379e0549b0a704d6a 100644
--- a/avocado/core/tree.py
+++ b/avocado/core/tree.py
@@ -59,7 +59,8 @@ class FilterSet(set):
                                               for item in items])
 
     def __str__(self):
-        return 'FilterSet([%s])' % ', '.join(["'%s'" % i for i in self])
+        return ('FilterSet([%s])'
+                % ', '.join(sorted(["'%s'" % i for i in self])))
 
 
 class TreeEnvironment(dict):