diff --git a/syntax/ats.vim b/syntax/ats.vim
index a11e016..22a9409 100644
--- a/syntax/ats.vim
+++ b/syntax/ats.vim
@@ -33,7 +33,7 @@ syn match atsArrow '=/=>'
 syn region atsArrow start="=<" end=">" contains=arrowContents
 syn region atsArrow start="-<" end=">"
 
-syn keyword atsType void bool string char int uint uint8 uint32 uint16 int8 int32 int16 charNZ strnptr Strptr0 Strptr1 nat lint ulint double float
+syn keyword atsType void bool string char int uint uint8 uint32 uint16 int8 int32 int16 charNZ strnptr Strptr0 Strptr1 nat lint ulint double float size_t
 syn keyword atsType datavtype datatype vtypedef dataviewtype viewtypdef typedef view viewdef dataview abstype absvtype absviewtype absview datasort dataprop type viewtype vtype
 syn keyword atsType absimpl
 syn keyword atsType implement primplmnt extern