diff --git a/servant/src/Servant/Types/SourceT.hs b/servant/src/Servant/Types/SourceT.hs
index d66405c5..11a9b027 100644
--- a/servant/src/Servant/Types/SourceT.hs
+++ b/servant/src/Servant/Types/SourceT.hs
@@ -269,7 +269,7 @@ mapMaybeStep p = go where
 
 -- | Run action for each value in the 'SourceT'.
 --
--- >>> foreach fail print (source "abc")
+-- >>> foreach fail print $ source ("abc" :: String)
 -- 'a'
 -- 'b'
 -- 'c'