diff --git a/Makefile b/Makefile
index 13b5f0a..2605c39 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,7 @@ check:
 coverage:
 	coverage erase
 	coverage run --source marshmallow_jsonschema -m py.test -v
+	coverage report -m
 
 pypitest:
 	python setup.py sdist upload -r pypitest
diff --git a/marshmallow_jsonschema/base.py b/marshmallow_jsonschema/base.py
index ffae465..fbda2aa 100644
--- a/marshmallow_jsonschema/base.py
+++ b/marshmallow_jsonschema/base.py
@@ -3,7 +3,8 @@
 import decimal
 
 from marshmallow import fields, missing, Schema, validate
-from marshmallow.compat import text_type, binary_type
+from marshmallow.class_registry import get_class
+from marshmallow.compat import text_type, binary_type, basestring
 
 from .validation import handle_length, handle_one_of, handle_range
 
@@ -144,7 +145,11 @@ def _from_python_type(cls, field, pytype):
 
     @classmethod
     def _from_nested_schema(cls, field):
-        schema = cls().dump(field.nested()).data
+        if isinstance(field.nested, basestring):
+            nested = get_class(field.nested)
+        else:
+            nested = field.nested
+        schema = cls().dump(nested()).data
 
         if field.metadata.get('metadata', {}).get('description'):
             schema['description'] = (
diff --git a/tests/test_dump.py b/tests/test_dump.py
index 4476fe9..039c72f 100644
--- a/tests/test_dump.py
+++ b/tests/test_dump.py
@@ -57,6 +57,22 @@ class TestNestedSchema(Schema):
     assert nested_dmp['title'] == 'Title1'
 
 
+def test_nested_string_to_cls():
+    class TestSchema(Schema):
+        foo = fields.Integer(required=True)
+
+    class TestNestedSchema(Schema):
+        foo2 = fields.Integer(required=True)
+        nested = fields.Nested('TestSchema')
+    schema = TestNestedSchema()
+    json_schema = JSONSchema()
+    dumped = json_schema.dump(schema).data
+    _validate_schema(dumped)
+    nested_json = dumped['properties']['nested']
+    assert nested_json['properties']['foo']['format'] == 'integer'
+    assert nested_json['type'] == 'object'
+
+
 def test_one_of_validator():
     schema = UserSchema()
     json_schema = JSONSchema()
@@ -64,6 +80,7 @@ def test_one_of_validator():
     _validate_schema(dumped)
     assert dumped['properties']['sex']['enum'] == ['male', 'female']
 
+
 def test_range_validator():
     schema = Address()
     json_schema = JSONSchema()