diff --git a/ox-rst.el b/ox-rst.el
index 1ab0d40..15a9029 100644
--- a/ox-rst.el
+++ b/ox-rst.el
@@ -170,7 +170,6 @@ When nil, an anchor with reference is used to link to the image."
 
 (defcustom org-rst-inline-image-rules
   '(("file" . "\\.\\(jpeg\\|jpg\\|png\\|webp\\|gif\\|svg\\|svgz\\|swf\\)\\'")
-    ("attachment" . "\\.\\(jpeg\\|jpg\\|png\\|webp\\|gif\\|svg\\|svgz\\|swf\\)\\'")
     ("http" . "\\.\\(jpeg\\|jpg\\|png\\|webp\\|gif\\|svg\\|svgz\\|swf\\)\\'")
     ("https" . "\\.\\(jpeg\\|jpg\\|png\\|webp\\|gif\\|svg\\|svgz\\|swf\\)\\'"))
   "Rules characterizing image files that can be inlined into reStructuredText.