diff --git a/stl/ast.py b/stl/ast.py
index 1721859..37d6a41 100644
--- a/stl/ast.py
+++ b/stl/ast.py
@@ -39,7 +39,7 @@ class _Top(AST):
         return "⊤"
 
     def __invert__(self):
-        return Bot()
+        return BOT
 
 
 class _Bot(AST):
@@ -47,7 +47,7 @@ class _Bot(AST):
         return "⊥"
 
     def __invert__(self):
-        return Top()
+        return TOP
 
 TOP = _Top()
 BOT = _Bot()
diff --git a/stl/test_ast.py b/stl/test_ast.py
index accbb9d..86d7cd3 100644
--- a/stl/test_ast.py
+++ b/stl/test_ast.py
@@ -11,3 +11,7 @@ class TestSTLAST(unittest.TestCase):
         self.assertEqual(stl.BOT, stl.BOT | stl.BOT)
         self.assertEqual(stl.TOP, stl.TOP | stl.BOT)
         self.assertEqual(stl.BOT, stl.TOP & stl.BOT)
+        self.assertEqual(~stl.BOT, stl.TOP)
+        self.assertEqual(~stl.TOP, stl.BOT)
+        self.assertEqual(~~stl.BOT, stl.BOT)
+        self.assertEqual(~~stl.TOP, stl.TOP)