diff --git a/loopy/preprocess.py b/loopy/preprocess.py
index ced1aaaa13ed8275c1e3a376d1c24895287b3239..541b44f58c5b02e9beba15211cb861fd09f14096 100644
--- a/loopy/preprocess.py
+++ b/loopy/preprocess.py
@@ -1928,7 +1928,7 @@ def find_idempotence(kernel):
             for insn in kernel.instructions)
 
     from collections import defaultdict
-    dep_graph = defaultdict(lambda: set())
+    dep_graph = defaultdict(set)
 
     for insn in kernel.instructions:
         dep_graph[insn.id] = set(writer_id
diff --git a/loopy/schedule/__init__.py b/loopy/schedule/__init__.py
index 518d850e997fe8435089832e2d3827ffab4bc373..d28e7b1b3def2b988b4624aed9caf8f65c70b2c5 100644
--- a/loopy/schedule/__init__.py
+++ b/loopy/schedule/__init__.py
@@ -1415,8 +1415,8 @@ class DependencyTracker(object):
             raise ValueError("unknown 'var_kind': %s" % var_kind)
 
         from collections import defaultdict
-        self.writer_map = defaultdict(lambda: set())
-        self.reader_map = defaultdict(lambda: set())
+        self.writer_map = defaultdict(set)
+        self.reader_map = defaultdict(set)
         self.temp_to_base_storage = kernel.get_temporary_to_base_storage_map()
 
     def map_to_base_storage(self, var_names):