diff --git a/stl/test_utils.py b/stl/test_utils.py
index 05a8960..38c2665 100644
--- a/stl/test_utils.py
+++ b/stl/test_utils.py
@@ -59,6 +59,14 @@ class TestSTLUtils(unittest.TestCase):
         post_l2 = len(list(stl.walk(stl.utils.f_neg_or_canonical_form(phi))))
         self.assertEqual(post_l, post_l2)
 
+    def test_andf(self):
+        phi = stl.parse("x")
+        self.assertEqual(phi, stl.andf(phi))
+
+    def test_orf(self):
+        phi = stl.parse("x")
+        self.assertEqual(phi, stl.orf(phi))
+
 #    def test_to_from_mtl(self):
 #        raise NotImplementedError
 
diff --git a/stl/utils.py b/stl/utils.py
index 5bcb6d5..6f169c9 100644
--- a/stl/utils.py
+++ b/stl/utils.py
@@ -131,10 +131,10 @@ def until(phi1, phi2, *, lo, hi):
     return stl.ast.Until(Interval(lo, hi), phi1, phi2)
 
 def andf(*args):
-    return reduce(op.and_, args, stl.TOP)
+    return reduce(op.and_, args) if args else stl.TOP
 
 def orf(*args):
-    return reduce(op.or_, args, stl.TOP)
+    return reduce(op.or_, args) if args else stl.TOP
 
 def implies(x, y):
     return ~x | y