diff --git a/Lib/_weakrefset.py b/Lib/_weakrefset.py
--- a/Lib/_weakrefset.py
+++ b/Lib/_weakrefset.py
@@ -60,6 +60,8 @@ class WeakSet(object):
             for itemref in self.data:
                 item = itemref()
                 if item is not None:
+                    # Caveat: the iterator will keep a strong reference to
+                    # `item` until it is resumed or closed.
                     yield item
 
     def __len__(self):
diff --git a/Lib/test/test_weakset.py b/Lib/test/test_weakset.py
--- a/Lib/test/test_weakset.py
+++ b/Lib/test/test_weakset.py
@@ -473,9 +473,14 @@ class TestWeakSet(unittest.TestCase):
         def testcontext():
             try:
                 it = iter(s)
-                next(it)
+                # Start iterator
+                yielded = ustr(str(next(it)))
                 # Schedule an item for removal and recreate it
                 u = ustr(str(items.pop()))
+                if yielded == u:
+                    # The iterator still has a reference to the removed item,
+                    # advance it (issue #20006).
+                    next(it)
                 gc.collect()      # just in case
                 yield u
             finally: