diff --git a/rest_framework/utils/field_mapping.py b/rest_framework/utils/field_mapping.py
index 9494b0af3..917c8458e 100644
--- a/rest_framework/utils/field_mapping.py
+++ b/rest_framework/utils/field_mapping.py
@@ -226,7 +226,7 @@ def get_relation_kwargs(field_name, relation_info):
             # No further keyword arguments are valid.
             return kwargs
 
-        if model_field.has_default() or model_field.null:
+        if model_field.has_default() or model_field.blank or model_field.null:
             kwargs['required'] = False
         if model_field.null:
             kwargs['allow_null'] = True