diff --git a/syntax/ats.vim b/syntax/ats.vim
index 42d6a58..e720d2c 100644
--- a/syntax/ats.vim
+++ b/syntax/ats.vim
@@ -72,7 +72,7 @@ syn keyword atsCond if then else case
 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 lam fix rec var of
+syn keyword atsStatement val and fnx fun fn lam fix rec var of assume
 syn keyword atsStatement begin end
 syn keyword atsTypedef typedef sortdef viewtypedef vtypedef
 syn keyword atsStructure datatype datavtype abstype dataviewtype dataprop dataview