diff --git a/utils/vim/syntax/llvm.vim b/utils/vim/syntax/llvm.vim
index 1a060ab6514..14987cb2348 100644
--- a/utils/vim/syntax/llvm.vim
+++ b/utils/vim/syntax/llvm.vim
@@ -89,6 +89,7 @@ syn keyword llvmKeyword
       \ hhvmcc
       \ hhvm_ccc
       \ hidden
+      \ immarg
       \ initialexec
       \ inlinehint
       \ inreg