diff --git a/atools/_memoize_decorator.py b/atools/_memoize_decorator.py
index 31d36f3..ac7e47b 100644
--- a/atools/_memoize_decorator.py
+++ b/atools/_memoize_decorator.py
@@ -11,6 +11,7 @@
 from time import time
 from threading import Lock as SyncLock
 from typing import Any, Callable, Dict, Hashable, Mapping, Optional, Tuple, Type, Union
+from weakref import WeakSet
 
 
 Decoratee = Union[Callable, Type]
@@ -492,7 +493,7 @@ def bar() -> Any: ...
     """
 
     _default_db_path = Path.home() / '.memoize'
-    _all_decorators = set()
+    _all_decorators = WeakSet()
 
     @staticmethod
     def __call__(
diff --git a/test/test_memoize_decorator.py b/test/test_memoize_decorator.py
index 2212b02..d072da2 100644
--- a/test/test_memoize_decorator.py
+++ b/test/test_memoize_decorator.py
@@ -903,3 +903,19 @@ def foo():
 
     assert foo() == PosixPath.cwd()
     assert isinstance(foo(), PosixPath)
+
+
+def test_memoized_function_is_deletable() -> None:
+    def get_foo() -> Callable[[], None]:
+        @memoize
+        def _foo() -> None:
+            ...
+
+        return _foo
+
+    foo = get_foo()
+    r = ref(foo)
+    assert r() is not None
+    del foo
+    # FIXME there's a race condition here. Garbage collector may not have cleaned up foo yet
+    assert r() is None