diff --git a/scrapy/trunk/scrapy/conf/core_settings.py b/scrapy/trunk/scrapy/conf/core_settings.py
index ad140af03..6f0186a9a 100644
--- a/scrapy/trunk/scrapy/conf/core_settings.py
+++ b/scrapy/trunk/scrapy/conf/core_settings.py
@@ -28,3 +28,6 @@ EXTENSIONS = []
 # contrib.middleware.retry.RetryMiddleware default settings
 RETRY_TIMES = 3
 RETRY_HTTP_CODES = ['500', '503', '504', '400', '408', '200']
+
+# amazon s3 images backend sometimes fails to authenticate or validate http protocol
+RETRY_HTTP_CODES = RETRY_HTTP_CODES + ['505', '403']