diff --git a/src/drf_yasg/utils.py b/src/drf_yasg/utils.py
index 96ba37e..d5f83ac 100644
--- a/src/drf_yasg/utils.py
+++ b/src/drf_yasg/utils.py
@@ -4,6 +4,7 @@ from django.core.validators import RegexValidator
 from django.utils.encoding import force_text
 from rest_framework import serializers
 from rest_framework.mixins import RetrieveModelMixin, DestroyModelMixin, UpdateModelMixin
+from rest_framework.settings import api_settings
 
 from . import openapi
 from .errors import SwaggerGenerationError
@@ -287,7 +288,13 @@ def serializer_field_to_swagger(field, swagger_object_type, definitions=None, **
         # swagger 2.0 does not support specifics about file fields, so ImageFile gets no special treatment
         # OpenAPI 3.0 does support it, so a future implementation could handle this better
         err = SwaggerGenerationError("parameter of type file is supported only in a formData Parameter")
-        if swagger_object_type != openapi.Parameter:
+        if swagger_object_type == openapi.Schema:
+            # FileField.to_representation returns URL or file name
+            if getattr(field, 'use_url', api_settings.UPLOADED_FILES_USE_URL):
+                return SwaggerType(type=openapi.TYPE_STRING, format=openapi.FORMAT_URI)
+            else:
+                return SwaggerType(type=openapi.TYPE_STRING)
+        elif swagger_object_type != openapi.Parameter:
             raise err  # pragma: no cover
         param = SwaggerType(type=openapi.TYPE_FILE)
         if param['in'] != openapi.IN_FORM:
diff --git a/testproj/articles/serializers.py b/testproj/articles/serializers.py
index 1509911..8403abd 100644
--- a/testproj/articles/serializers.py
+++ b/testproj/articles/serializers.py
@@ -12,8 +12,8 @@ class ArticleSerializer(serializers.ModelSerializer):
 
     class Meta:
         model = Article
-        fields = ('title', 'body', 'slug', 'date_created', 'date_modified', 'references', 'uuid')
-        read_only_fields = ('date_created', 'date_modified')
+        fields = ('title', 'body', 'slug', 'date_created', 'date_modified', 'references', 'uuid', 'cover')
+        read_only_fields = ('date_created', 'date_modified', 'cover')
         lookup_field = 'slug'
         extra_kwargs = {'body': {'help_text': 'body serializer help_text'}}
 
diff --git a/tests/reference.yaml b/tests/reference.yaml
index 40bef95..b147844 100644
--- a/tests/reference.yaml
+++ b/tests/reference.yaml
@@ -493,6 +493,10 @@ definitions:
         description: should articles have UUIDs?
         type: string
         format: uuid
+      cover:
+        type: string
+        format: uri
+        readOnly: true
   Project:
     required:
       - project_name