diff --git a/src/testdir/test_hlsearch.vim b/src/testdir/test_hlsearch.vim
index 066fdd0..b934d38 100644
--- a/src/testdir/test_hlsearch.vim
+++ b/src/testdir/test_hlsearch.vim
@@ -32,3 +32,21 @@
   call getchar(1)
   enew!
 endfunction
+
+func Test_hlsearch_hangs()
+  if !has('reltime') || !has('float')
+    return
+  endif
+
+  " This pattern takes forever to match, it should timeout.
+  help
+  let start = reltime()
+  set hlsearch nolazyredraw redrawtime=101
+  let @/ = '\%#=2\v(a|\1)*'
+  redraw
+  let elapsed = reltimefloat(reltime(start))
+  call assert_true(elapsed > 0.1)
+  call assert_true(elapsed < 1.0)
+  set nohlsearch redrawtime&
+  quit
+endfunc
diff --git a/src/version.c b/src/version.c
index 268d4d7..24bb820 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    644,
+/**/
     643,
 /**/
     642,