diff --git a/scrapy/extensions/throttle.py b/scrapy/extensions/throttle.py
index 46273353b..d2ff8665e 100644
--- a/scrapy/extensions/throttle.py
+++ b/scrapy/extensions/throttle.py
@@ -28,7 +28,7 @@ class AutoThrottle(object):
 
     def _min_delay(self, spider):
         s = self.crawler.settings
-        return getattr(spider, 'download_delay', 0.0) or s.getfloat('DOWNLOAD_DELAY')
+        return getattr(spider, 'download_delay', s.getfloat('DOWNLOAD_DELAY'))
 
     def _max_delay(self, spider):
         return self.crawler.settings.getfloat('AUTOTHROTTLE_MAX_DELAY')