diff --git a/heat/engine/constraints.py b/heat/engine/constraints.py
index 60dff634d1..2da0b39e36 100644
--- a/heat/engine/constraints.py
+++ b/heat/engine/constraints.py
@@ -173,8 +173,6 @@ class Schema(collections.Mapping):
             elif self.type == self.NUMBER:
                 return Schema.str_to_num(value)
             elif self.type == self.STRING:
-                if value and not isinstance(value, basestring):
-                    raise ValueError()
                 return str(value)
             elif self.type == self.BOOLEAN:
                 return strutils.bool_from_string(str(value), strict=True)
diff --git a/heat/tests/test_constraints.py b/heat/tests/test_constraints.py
index 7c77f70b3e..5c3550fd60 100644
--- a/heat/tests/test_constraints.py
+++ b/heat/tests/test_constraints.py
@@ -390,9 +390,12 @@ class SchemaTest(testtools.TestCase):
         self.assertIsInstance(res, basestring)
         res = schema.to_schema_type('1')
         self.assertIsInstance(res, basestring)
-        err = self.assertRaises(ValueError, schema.to_schema_type, 1)
-        self.assertEqual('Value "1" is invalid for data type "String".',
-                         six.text_type(err))
+        res = schema.to_schema_type(1)
+        self.assertIsInstance(res, basestring)
+        res = schema.to_schema_type(True)
+        self.assertIsInstance(res, basestring)
+        res = schema.to_schema_type(None)
+        self.assertIsInstance(res, basestring)
 
     def test_to_schema_type_boolean(self):
         '''Test Schema.to_schema_type method for type Boolean.'''