diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 7e04e7e47e3..2b7906a593e 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -280,7 +280,7 @@ def get_url(self, obj, view_name, request, format):
         attributes are not configured to correctly match the URL conf.
         """
         # Unsaved objects will not yet have a valid URL.
-        if hasattr(obj, 'pk') and obj.pk is None:
+        if hasattr(obj, 'pk') and obj.pk in (None, ''):
             return None
 
         lookup_value = getattr(obj, self.lookup_field)
diff --git a/tests/test_relations.py b/tests/test_relations.py
index 24087839489..f49e4ed143c 100644
--- a/tests/test_relations.py
+++ b/tests/test_relations.py
@@ -87,6 +87,19 @@ def test_pk_representation(self):
         assert representation == self.instance.pk.int
 
 
+class TestHyperlinkedRelatedField(APISimpleTestCase):
+    def setUp(self):
+        self.instance = MockObject(pk=1, name='foo')
+        self.field = serializers.HyperlinkedRelatedField(
+            view_name='example', read_only=True)
+        self.field.reverse = mock_reverse
+        self.field._context = {'request': True}
+
+    def test_representation_unsaved_object_with_non_nullable_pk(self):
+        representation = self.field.to_representation(MockObject(pk=''))
+        assert representation is None
+
+
 class TestHyperlinkedIdentityField(APISimpleTestCase):
     def setUp(self):
         self.instance = MockObject(pk=1, name='foo')