diff --git a/NEWS b/NEWS
index 5dbc3bcbc..302227ff1 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,7 @@
+0.0.7-dev
+
+ * Improved mocking of Python builtins in unit tests.
+
 0.0.6
 
  * New configuration section for customizing which Attic consistency checks run, if any.
diff --git a/atticmatic/config.py b/atticmatic/config.py
index 8254c8804..7474f0502 100644
--- a/atticmatic/config.py
+++ b/atticmatic/config.py
@@ -143,7 +143,7 @@ def parse_configuration(config_filename):
     Raise IOError if the file cannot be read, or ValueError if the format is not as expected.
     '''
     parser = ConfigParser()
-    parser.readfp(open(config_filename))
+    parser.read(config_filename)
 
     validate_configuration_format(parser, CONFIG_FORMAT)
 
diff --git a/atticmatic/tests/builtins.py b/atticmatic/tests/builtins.py
new file mode 100644
index 000000000..ff48f939b
--- /dev/null
+++ b/atticmatic/tests/builtins.py
@@ -0,0 +1,11 @@
+from flexmock import flexmock
+import sys
+
+
+def builtins_mock():
+    try:
+        # Python 2
+        return flexmock(sys.modules['__builtin__'])
+    except KeyError:
+        # Python 3
+        return flexmock(sys.modules['builtins'])
diff --git a/atticmatic/tests/unit/test_attic.py b/atticmatic/tests/unit/test_attic.py
index 26c629984..ab52850c4 100644
--- a/atticmatic/tests/unit/test_attic.py
+++ b/atticmatic/tests/unit/test_attic.py
@@ -3,6 +3,7 @@ from collections import OrderedDict
 from flexmock import flexmock
 
 from atticmatic import attic as module
+from atticmatic.tests.builtins import builtins_mock
 
 
 def insert_subprocess_mock(check_call_command, **kwargs):
@@ -18,7 +19,7 @@ def insert_subprocess_never():
 
 
 def insert_platform_mock():
-    flexmock(module).platform = flexmock().should_receive('node').and_return('host').mock
+    flexmock(module.platform).should_receive('node').and_return('host')
 
 
 def insert_datetime_mock():
@@ -166,8 +167,8 @@ def test_check_archives_should_call_attic_with_parameters():
     )
     insert_platform_mock()
     insert_datetime_mock()
-    flexmock(module).open = lambda filename, mode: stdout
-    flexmock(module).os = flexmock().should_receive('devnull').mock
+    builtins_mock().should_receive('open').and_return(stdout)
+    flexmock(module.os).should_receive('devnull')
 
     module.check_archives(
         verbose=False,
@@ -204,5 +205,3 @@ def test_check_archives_without_any_checks_should_bail():
         repository='repo',
         consistency_config=consistency_config,
     )
-
-
diff --git a/atticmatic/tests/unit/test_config.py b/atticmatic/tests/unit/test_config.py
index 1c9fcb654..02f1f521b 100644
--- a/atticmatic/tests/unit/test_config.py
+++ b/atticmatic/tests/unit/test_config.py
@@ -197,9 +197,8 @@ def test_parse_section_options_for_missing_section_should_return_empty_dict():
 
 def insert_mock_parser():
     parser = flexmock()
-    parser.should_receive('readfp')
-    flexmock(module).open = lambda filename: None
-    flexmock(module).ConfigParser = parser
+    parser.should_receive('read')
+    module.ConfigParser = lambda: parser
 
     return parser