diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index fa6a6f0bb..e2ea0d744 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -398,6 +398,10 @@ class Serializer(BaseSerializer):
 
     def get_initial(self):
         if hasattr(self, 'initial_data'):
+            # initial_data may not be a valid type
+            if not isinstance(self.initial_data, Mapping):
+                return OrderedDict()
+
             return OrderedDict([
                 (field_name, field.get_value(self.initial_data))
                 for field_name, field in self.fields.items()