diff --git a/src/testdir/gen_opt_test.vim b/src/testdir/gen_opt_test.vim
index faff33a..271abed 100644
--- a/src/testdir/gen_opt_test.vim
+++ b/src/testdir/gen_opt_test.vim
@@ -73,7 +73,7 @@
       \ 'buftype': [['', 'help', 'nofile'], ['xxx', 'help,nofile']],
       \ 'casemap': [['', 'internal'], ['xxx']],
       \ 'cedit': [['', '\<Esc>'], ['xxx', 'f']],
-      \ 'clipboard': [['', 'unnamed', 'autoselect,unnamed', 'html', 'exclude:vimdisplay'], ['xxx', '\ze*']],
+      \ 'clipboard': [['', 'unnamed', 'autoselect,unnamed', 'html', 'exclude:vimdisplay'], ['xxx', '\ze*', 'exclude:\\%(']],
       \ 'colorcolumn': [['', '8', '+2'], ['xxx']],
       \ 'comments': [['', 'b:#'], ['xxx']],
       \ 'commentstring': [['', '/*%s*/'], ['xxx']],
diff --git a/src/testdir/test_arglist.vim b/src/testdir/test_arglist.vim
index 9b23a51..615d816 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -425,6 +425,7 @@
   call assert_equal(['b'], argv())
   call assert_fails('argdelete', 'E610:')
   call assert_fails('1,100argdelete', 'E16:')
+  call assert_fails('argdel /\)/', 'E55:')
 
   call Reset_arglist()
   args a b c d
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index b7067a7..b7cc0c0 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -2520,6 +2520,7 @@
   call assert_fails('doautocmd * BufEnter', 'E217:')
   call assert_fails('augroup! x1a2b3', 'E367:')
   call assert_fails('autocmd BufNew <buffer=999> pwd', 'E680:')
+  call assert_fails('autocmd BufNew \) set ff=unix', 'E55:')
 endfunc
 
 " Test for deep nesting of autocmds
diff --git a/src/testdir/test_buffer.vim b/src/testdir/test_buffer.vim
index e54b633..8ef41e2 100644
--- a/src/testdir/test_buffer.vim
+++ b/src/testdir/test_buffer.vim
@@ -138,6 +138,7 @@
   %bwipe!
   call assert_fails('bdelete 5', 'E516:')
   call assert_fails('1,1bdelete 1 2', 'E488:')
+  call assert_fails('bdelete \)', 'E55:')
 
   " Deleting a unlisted and unloaded buffer
   edit Xfile1
diff --git a/src/testdir/test_checkpath.vim b/src/testdir/test_checkpath.vim
index 28e9105..f6a3bbc 100644
--- a/src/testdir/test_checkpath.vim
+++ b/src/testdir/test_checkpath.vim
@@ -103,4 +103,19 @@
   set includeexpr&
 endfunc
 
+" Test for invalid regex in 'include' and 'define' options
+func Test_checkpath_errors()
+  let save_include = &include
+  set include=\\%(
+  call assert_fails('checkpath', 'E53:')
+  let &include = save_include
+
+  let save_define = &define
+  set define=\\%(
+  call assert_fails('dsearch abc', 'E53:')
+  let &define = save_define
+
+  call assert_fails('psearch \%(', 'E53:')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index a547ac4..026625e 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -185,6 +185,8 @@
   unmap <Left>
   set cpo-=k
 
+  call assert_fails('call feedkeys(":map \\\\%(\<Tab>\<Home>\"\<CR>", "xt")', 'E53:')
+
   unmap <Middle>x
   set cpo&vim
 endfunc
diff --git a/src/testdir/test_debugger.vim b/src/testdir/test_debugger.vim
index 8c51675..b6231cf 100644
--- a/src/testdir/test_debugger.vim
+++ b/src/testdir/test_debugger.vim
@@ -339,6 +339,7 @@
   call delete('Xtest.vim')
   %bw!
   call assert_fails('breakadd here', 'E32:')
+  call assert_fails('breakadd file Xtest.vim /\)/', 'E55:')
 endfunc
 
 func Test_Backtrace_Through_Source()
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 2492c93..5e4eacd 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -973,6 +973,7 @@
   call assert_equal(4,  match('testing', 'ing', -1))
   call assert_fails("let x=match('testing', 'ing', 0, [])", 'E745:')
   call assert_equal(-1, match(test_null_list(), 2))
+  call assert_equal(-1, match('abc', '\\%('))
 endfunc
 
 func Test_matchend()
diff --git a/src/testdir/test_history.vim b/src/testdir/test_history.vim
index feb521e..1bea78d 100644
--- a/src/testdir/test_history.vim
+++ b/src/testdir/test_history.vim
@@ -95,6 +95,7 @@
   call assert_fails('call histnr([])', 'E730:')
   call assert_fails('history xyz', 'E488:')
   call assert_fails('history ,abc', 'E488:')
+  call assert_fails('call histdel(":", "\\%(")', 'E53:')
 endfunction
 
 function Test_Search_history_window()
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 66b8406..63fa04e 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -753,6 +753,7 @@
   call assert_equal(['', 'a', '', 'b', '', 'c', ''], split('abc', '\zs', 1))
   call assert_fails("call split('abc', [])", 'E730:')
   call assert_fails("call split('abc', 'b', [])", 'E745:')
+  call assert_equal(['abc'], split('abc', '\\%('))
 endfunc
 
 " compare recursively linked list and dict
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index ec40ccc..22e0809 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -411,6 +411,7 @@
     call assert_fails('set pyxversion=6', 'E474:')
   endif
   call assert_fails("let &tabstop='ab'", 'E521:')
+  call assert_fails('set spellcapcheck=%\\(', 'E54:')
 endfunc
 
 func CheckWasSet(name)
diff --git a/src/testdir/test_search_stat.vim b/src/testdir/test_search_stat.vim
index 73cea03..2afccef 100644
--- a/src/testdir/test_search_stat.vim
+++ b/src/testdir/test_search_stat.vim
@@ -260,6 +260,14 @@
 
 func Test_searchcount_fails()
   call assert_fails('echo searchcount("boo!")', 'E715:')
+  call assert_fails('echo searchcount({"timeout" : []})', 'E745:')
+  call assert_fails('echo searchcount({"maxcount" : []})', 'E745:')
+  call assert_fails('echo searchcount({"pattern" : []})', 'E730:')
+  call assert_fails('echo searchcount({"pos" : 1})', 'E475:')
+  call assert_fails('echo searchcount({"pos" : [1]})', 'E475:')
+  call assert_fails('echo searchcount({"pos" : [[], 2, 3]})', 'E745:')
+  call assert_fails('echo searchcount({"pos" : [1, [], 3]})', 'E745:')
+  call assert_fails('echo searchcount({"pos" : [1, 2, []]})', 'E745:')
 endfunc
 
 func Test_searchcount_in_statusline()
diff --git a/src/testdir/test_sort.vim b/src/testdir/test_sort.vim
index c7504b7..d76132e 100644
--- a/src/testdir/test_sort.vim
+++ b/src/testdir/test_sort.vim
@@ -1256,6 +1256,7 @@
   call assert_fails('sort no', 'E474:')
   call assert_fails('sort c', 'E475:')
   call assert_fails('sort #pat%', 'E654:')
+  call assert_fails('sort /\%(/', 'E53:')
 
   enew!
 endfunc
diff --git a/src/testdir/test_substitute.vim b/src/testdir/test_substitute.vim
index a137aa5..f38eb55 100644
--- a/src/testdir/test_substitute.vim
+++ b/src/testdir/test_substitute.vim
@@ -246,6 +246,7 @@
   call assert_fails("let s=substitute('abcda', [], 'A', 'g')", 'E730:')
   call assert_fails("let s=substitute('abcda', 'a', [], 'g')", 'E730:')
   call assert_fails("let s=substitute('abcda', 'a', 'A', [])", 'E730:')
+  call assert_fails("let s=substitute('abc', '\\%(', 'A', 'g')", 'E53:')
 
   bwipe!
 endfunc
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index 8a02185..dc05355 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -373,6 +373,7 @@
   call AssertFails('syntax cluster contains=Abc', 'E400:')
   call AssertFails("syntax match Character /'.'", 'E401:')
   call AssertFails("syntax match Character /'.'/a", 'E402:')
+  call assert_fails('syntax sync linecont /\%(/', 'E53:')
   call assert_fails('syntax sync linecont /pat', 'E404:')
   call assert_fails('syntax sync linecont', 'E404:')
   call assert_fails('syntax sync linecont /pat1/ linecont /pat2/', 'E403:')
@@ -382,6 +383,7 @@
   call AssertFails('syntax match ccFoo "Foo" nextgroup=ALLBUT,F', 'E407:')
   call AssertFails('syntax region Block start="{" contains=F,ALLBUT', 'E408:')
   call AssertFails("syntax match Characters contains=a.*x /'.'/", 'E409:')
+  call assert_fails('syntax match Search /abc/ contains=ALLBUT,/\%(/', 'E53:')
 endfunc
 
 func Test_syn_sync()
diff --git a/src/testdir/test_tagjump.vim b/src/testdir/test_tagjump.vim
index ab4841f..a872b1c 100644
--- a/src/testdir/test_tagjump.vim
+++ b/src/testdir/test_tagjump.vim
@@ -184,6 +184,10 @@
   call search("start")
   exe "normal! 5\<C-W>\<C-I>"
   call assert_equal("		start OK if found this line", getline('.'))
+
+  " invalid tag search pattern
+  call assert_fails('tag /\%(/', 'E426:')
+
   enew! | only
   call delete('Xtestfile')
   call delete('Xinclude')
diff --git a/src/testdir/test_user_func.vim b/src/testdir/test_user_func.vim
index ed07d99..2edaec8 100644
--- a/src/testdir/test_user_func.vim
+++ b/src/testdir/test_user_func.vim
@@ -410,6 +410,9 @@
   call writefile(['func foo#Bar()', 'return 1', 'endfunc'], 'Xscript')
   call assert_fails('source Xscript', 'E746:')
   call delete('Xscript')
+
+  " Try to list functions using an invalid search pattern
+  call assert_fails('function /\%(/', 'E53:')
 endfunc
 
 " Test for deleting a function
diff --git a/src/version.c b/src/version.c
index d85ac1b..a2383c9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1736,
+/**/
     1735,
 /**/
     1734,