diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+#### 0.36.0.5
+
+* Fix documentation for `fileO`.
+
 #### 0.36.0.4
 
 * Drop (internal) dependency on either, this removes 20(!) transitive
diff --git a/rest-core.cabal b/rest-core.cabal
--- a/rest-core.cabal
+++ b/rest-core.cabal
@@ -1,5 +1,5 @@
 name:                rest-core
-version:             0.36.0.4
+version:             0.36.0.5
 description:         Rest API library.
 synopsis:            Rest API library.
 maintainer:          code@silk.co
diff --git a/src/Rest/Dictionary/Combinators.hs b/src/Rest/Dictionary/Combinators.hs
--- a/src/Rest/Dictionary/Combinators.hs
+++ b/src/Rest/Dictionary/Combinators.hs
@@ -145,7 +145,11 @@
 stringO :: Dict h p i Nothing e -> Dict h p i (Just String) e
 stringO = L.set outputs (Dicts [StringO])
 
--- | Allow file output using a combination of the raw data and a mime type.
+-- | Allow file output using a combination of the raw data, the file
+-- name, and an attachment flag (causing the file to be downloaded by
+-- browsers instead of shown). The mime type will be determined from
+-- the file extension by your web server library, or
+-- "application/octet-stream" with an unknown extension.
 
 fileO :: Dict h p i Nothing e -> Dict h p i (Just (ByteString, String, Bool)) e
 fileO = L.set outputs (Dicts [FileO])