diff --git a/syntax/ats.vim b/syntax/ats.vim
index 901515d..453dec6 100644
--- a/syntax/ats.vim
+++ b/syntax/ats.vim
@@ -67,7 +67,7 @@ syn keyword atsCond if then else case sif when
 syn keyword atsRepeat while
 syn keyword atsException exception raise try
 syn keyword atsStatement let in where local
-syn keyword atsStatement val and fnx fun fn llam lam fix rec var of assume castfn prfun
+syn keyword atsStatement val and fnx fun fn llam lam fix rec var of assume castfn prfun prfn
 syn keyword atsStatement begin end
 syn keyword atsTypedef typedef sortdef viewtypedef vtypedef viewdef
 syn keyword atsStructure datatype datavtype abstype dataviewtype dataprop dataview