diff --git a/llvm/utils/vim/syntax/llvm.vim b/llvm/utils/vim/syntax/llvm.vim
--- a/llvm/utils/vim/syntax/llvm.vim
+++ b/llvm/utils/vim/syntax/llvm.vim
@@ -211,7 +211,7 @@
 syn match   llvmFloat  /-\?\<\d\+\.\d*\(e[+-]\d\+\)\?\>/
 syn match   llvmFloat  /\<0x\x\+\>/
 syn keyword llvmBoolean true false
-syn keyword llvmConstant zeroinitializer undef null none
+syn keyword llvmConstant zeroinitializer undef null none poison
 syn match   llvmComment /;.*$/
 syn region  llvmString start=/"/ skip=/\\"/ end=/"/
 syn match   llvmLabel /[-a-zA-Z$._][-a-zA-Z$._0-9]*:/