diff --git a/storages/backends/s3boto3.py b/storages/backends/s3boto3.py
index 6c18ced60..727782f76 100644
--- a/storages/backends/s3boto3.py
+++ b/storages/backends/s3boto3.py
@@ -501,7 +501,7 @@ def size(self, name):
         if self.entries:
             entry = self.entries.get(name)
             if entry:
-                return entry.size
+                return entry.size if hasattr(entry, 'size') else entry.content_length
             return 0
         return self.bucket.Object(self._encode_name(name)).content_length