diff --git a/runtime/syntax/haredoc.vim b/runtime/syntax/haredoc.vim
new file mode 100644
index 0000000..09c99c1
--- /dev/null
+++ b/runtime/syntax/haredoc.vim
@@ -0,0 +1,32 @@
+" Vim syntax file.
+" Language:    Haredoc (Hare documentation format)
+" Maintainer:  Amelia Clarke <selene@perilune.dev>
+" Last Change: 2024-05-10
+" Upstream:    https://git.sr.ht/~selene/hare.vim
+
+if exists('b:current_syntax')
+  finish
+endif
+let b:current_syntax = 'haredoc'
+
+" Syntax {{{1
+syn case match
+syn iskeyword @,48-57,_
+
+" Code samples.
+syn region haredocCodeSample excludenl start='\t\zs' end='$' contains=@NoSpell display
+
+" References to other declarations and modules.
+syn region haredocRef start='\[\[' end=']]' contains=haredocRefValid,@NoSpell display keepend oneline
+syn match haredocRefValid '\v\[\[\h\w*%(::\h\w*)*%(::)?]]' contained contains=@NoSpell display
+
+" Miscellaneous.
+syn keyword haredocTodo FIXME TODO XXX
+
+" Default highlighting {{{1
+hi def link haredocCodeSample Comment
+hi def link haredocRef Error
+hi def link haredocRefValid Special
+hi def link haredocTodo Todo
+
+" vim: et sts=2 sw=2 ts=8