diff --git a/src/flake8/main/application.py b/src/flake8/main/application.py
index d7719e3..293ac92 100644
--- a/src/flake8/main/application.py
+++ b/src/flake8/main/application.py
@@ -261,7 +261,7 @@ class Application(object):
             List of filenames to process
         """
         if self.running_against_diff:
-            files = sorted(self.parsed_diff.keys())
+            files = sorted(self.parsed_diff)
         self.file_checker_manager.start(files)
         self.file_checker_manager.run()
         LOG.info('Finished running')
diff --git a/src/flake8/main/vcs.py b/src/flake8/main/vcs.py
index 6f7499e..207d26c 100644
--- a/src/flake8/main/vcs.py
+++ b/src/flake8/main/vcs.py
@@ -36,4 +36,4 @@ def install(option, option_string, value, parser):
 
 def choices():
     """Return the list of VCS choices."""
-    return list(_INSTALLERS.keys())
+    return list(_INSTALLERS)
diff --git a/src/flake8/plugins/_trie.py b/src/flake8/plugins/_trie.py
index 4871abb..17c226f 100644
--- a/src/flake8/plugins/_trie.py
+++ b/src/flake8/plugins/_trie.py
@@ -90,7 +90,7 @@ class TrieNode(object):
         if not self.children:
             return
 
-        for prefix in sorted(self.children.keys()):
+        for prefix in sorted(self.children):
             child = self.children[prefix]
             yield child
             for child in child.traverse():
diff --git a/src/flake8/statistics.py b/src/flake8/statistics.py
index 45a7eb1..d555df2 100644
--- a/src/flake8/statistics.py
+++ b/src/flake8/statistics.py
@@ -17,7 +17,7 @@ class Statistics(object):
         :rtype:
             list(str)
         """
-        return sorted({key.code for key in self._store.keys()})
+        return sorted({key.code for key in self._store})
 
     def record(self, error):
         """Add the fact that the error was seen in the file.
@@ -55,7 +55,7 @@ class Statistics(object):
         :returns:
             Generator of instances of :class:`Statistic`
         """
-        matching_errors = sorted(key for key in self._store.keys()
+        matching_errors = sorted(key for key in self._store
                                  if key.matches(prefix, filename))
         for error_code in matching_errors:
             yield self._store[error_code]
diff --git a/tests/unit/test_plugin_type_manager.py b/tests/unit/test_plugin_type_manager.py
index 186c2e3..4e69cee 100644
--- a/tests/unit/test_plugin_type_manager.py
+++ b/tests/unit/test_plugin_type_manager.py
@@ -205,7 +205,7 @@ class FakePluginTypeManager(manager.NotifierBuilderMixin):
 
     def __init__(self, manager):
         """Initialize with our fake manager."""
-        self.names = sorted(manager.keys())
+        self.names = sorted(manager)
         self.manager = manager