diff --git a/CHANGES.md b/CHANGES.md
index 0d650fd..9fe1747 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,9 @@
 # Revision History
 
+## 0.6.1 (2015/02/23)
+
+- Fixed handling of `None` in `NullableString`.
+
 ## 0.6 (2015/02/23)
 
 - Added preliminary support for JSON serialization (@pr0xmeh).
diff --git a/yorm/__init__.py b/yorm/__init__.py
index 050d0a9..7b14660 100644
--- a/yorm/__init__.py
+++ b/yorm/__init__.py
@@ -3,7 +3,7 @@
 import sys
 
 __project__ = 'YORM'
-__version__ = '0.6'
+__version__ = '0.6.1'
 
 VERSION = __project__ + '-' + __version__
 
diff --git a/yorm/test/__init__.py b/yorm/test/__init__.py
index 2e47072..031a459 100644
--- a/yorm/test/__init__.py
+++ b/yorm/test/__init__.py
@@ -7,6 +7,10 @@
 import expecter
 
 
+def is_none(x):
+    return x is None
+
+
 def is_true(x):
     return x is True
 
@@ -23,6 +27,7 @@ def missing(x):
     return not os.path.exists(x)
 
 
+expecter.add_expectation(is_none)
 expecter.add_expectation(is_true)
 expecter.add_expectation(is_false)
 expecter.add_expectation(exists)
diff --git a/yorm/test/test_types_extended.py b/yorm/test/test_types_extended.py
index bba2699..d0d902c 100644
--- a/yorm/test/test_types_extended.py
+++ b/yorm/test/test_types_extended.py
@@ -1,10 +1,12 @@
-# pylint: disable=missing-docstring,no-self-use,misplaced-comparison-constant
+# pylint: disable=missing-docstring,unused-variable,misplaced-comparison-constant,no-self-use
 
 import pytest
+from expecter import expect
 
 from yorm.utilities import attr
-from yorm.types import Integer, String, Float
-from yorm.types.extended import Markdown, AttributeDictionary, SortedList
+from yorm.types.standard import Integer, String, Float
+from yorm.types.extended import (NullableString, Markdown,
+                                 AttributeDictionary, SortedList)
 
 
 # CLASSES ######################################################################
@@ -37,6 +39,20 @@ class UnknownSortedList(SortedList):
 # TESTS ########################################################################
 
 
+def describe_nullable_string():
+
+    def describe_to_value():
+
+        def it_allows_none():
+            expect(NullableString.to_value(None)).is_none()
+
+    def describe_to_data():
+
+        def it_allows_none():
+            expect(NullableString.to_data(None)).is_none()
+
+
+# TODO: make these tests look like `test_types_standard.py`
 class TestMarkdown:
 
     """Unit tests for the `Markdown` converter."""
diff --git a/yorm/types/standard.py b/yorm/types/standard.py
index e7768e3..abd4efa 100644
--- a/yorm/types/standard.py
+++ b/yorm/types/standard.py
@@ -53,7 +53,7 @@ def _optimize_for_quoting(value):
         for num in (int, float):
             try:
                 return num(value)
-            except ValueError:
+            except (TypeError, ValueError):
                 continue
         return value