diff --git a/bugbear.py b/bugbear.py
index 358c02f..06e598d 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -824,6 +824,11 @@ def visit_DictComp(self, node):
     def visit_comprehension(self, node):
         self.visit(node.iter)
 
+    def visit_Lambda(self, node):
+        self.visit(node.body)
+        for lambda_arg in node.args.args:
+            self.names.pop(lambda_arg.arg, None)
+
 
 error = namedtuple("error", "lineno col message type vars")
 Error = partial(partial, error, type=BugBearChecker, vars=())
diff --git a/tests/b020.py b/tests/b020.py
index 4f30984..9bdc4b4 100644
--- a/tests/b020.py
+++ b/tests/b020.py
@@ -35,3 +35,6 @@
 # However we still call out reassigning the iterable in the comprehension.
 for vars in [i for i in vars]:
     print(vars)
+
+for var in sorted(range(10), key=lambda var: var.real):
+    print(var)