diff --git a/easy_thumbnails/files.py b/easy_thumbnails/files.py
index 7711541f..73726624 100644
--- a/easy_thumbnails/files.py
+++ b/easy_thumbnails/files.py
@@ -415,6 +415,12 @@ def get_thumbnail_modtime(self, thumbnail_name):
         except NotImplementedError:
             return None
 
+    def open(self, mode='rb'):
+        self.file.open(mode)
+
+    # open() doesn't alter the file's contents, but it does reset the pointer.
+    open.alters_data = True
+
 
 class ThumbnailerFieldFile(FieldFile, Thumbnailer):
     """