diff --git a/haystack/query.py b/haystack/query.py
index 1be64658f..7b2e71076 100644
--- a/haystack/query.py
+++ b/haystack/query.py
@@ -86,7 +86,7 @@ def __len__(self):
                 self._result_count = 0
 
         # This needs to return the actual number of hits, not what's in the cache.
-        return self._result_count - self._ignored_result_count
+        return max(self._result_count - self._ignored_result_count, 0)
 
     def __iter__(self):
         if self._cache_is_full():