diff --git a/stl/ast.py b/stl/ast.py
index 37d6a41..6ed256a 100644
--- a/stl/ast.py
+++ b/stl/ast.py
@@ -15,10 +15,13 @@ t_sym = Symbol('t', positive=True)
 def flatten_binary(phi, op, dropT, shortT):
     f = lambda x: x.args if isinstance(x, op) else [x]
     args = [arg for arg in phi.args if arg is not dropT]
+
     if any(arg is shortT for arg in args):
         return shortT
     elif not args:
         return dropT
+    elif len(args) == 1:
+        return args[0]
     else:
         return op(tuple(fn.mapcat(f, phi.args)))
         
diff --git a/stl/test_ast.py b/stl/test_ast.py
index 86d7cd3..9beb3c7 100644
--- a/stl/test_ast.py
+++ b/stl/test_ast.py
@@ -7,6 +7,10 @@ class TestSTLAST(unittest.TestCase):
         phi = stl.parse("x")
         self.assertEqual(stl.TOP, stl.TOP | phi)
         self.assertEqual(stl.BOT, stl.BOT & phi)
+        self.assertEqual(stl.TOP, phi | stl.TOP)
+        self.assertEqual(stl.BOT, phi & stl.BOT)
+        self.assertEqual(phi, phi & stl.TOP)
+        self.assertEqual(phi, phi | stl.BOT)
         self.assertEqual(stl.TOP, stl.TOP & stl.TOP)
         self.assertEqual(stl.BOT, stl.BOT | stl.BOT)
         self.assertEqual(stl.TOP, stl.TOP | stl.BOT)