diff --git a/ci/build.ps1 b/ci/build.ps1
index 01cf20874e..36570be7ae 100644
--- a/ci/build.ps1
+++ b/ci/build.ps1
@@ -36,8 +36,7 @@ $scoop = (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh'
   Invoke-Expression $scoop
 }
 
-scoop install diffutils perl
-diff3 --version
+scoop install perl
 perl --version
 cpanm.bat --version
 
@@ -81,7 +80,7 @@ if ($compiler -eq 'MINGW') {
   # in MSYS2, but we cannot build inside the MSYS2 shell.
   $cmakeGenerator = 'Ninja'
   $cmakeGeneratorArgs = '-v'
-  $mingwPackages = @('ninja', 'cmake').ForEach({
+  $mingwPackages = @('ninja', 'cmake', 'diffutils').ForEach({
     "mingw-w64-$arch-$_"
   })
 
diff --git a/runtime/scripts.vim b/runtime/scripts.vim
index a690431014..c552f0202f 100644
--- a/runtime/scripts.vim
+++ b/runtime/scripts.vim
@@ -376,6 +376,10 @@ else
   elseif s:line1 =~? '-\*-.*erlang.*-\*-'
     set ft=erlang
 
+  " YAML
+  elseif s:line1 =~# '^%YAML'
+    set ft=yaml
+
   " CVS diff
   else
     let s:lnum = 1
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index f5c5ef9e97..ca0e078e4a 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -8114,10 +8114,16 @@ void get_system_output_as_rettv(typval_T *argvars, typval_T *rettv,
 bool callback_from_typval(Callback *const callback, typval_T *const arg)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
 {
+  int r = OK;
+
   if (arg->v_type == VAR_PARTIAL && arg->vval.v_partial != NULL) {
     callback->data.partial = arg->vval.v_partial;
     callback->data.partial->pt_refcount++;
     callback->type = kCallbackPartial;
+  } else if (arg->v_type == VAR_STRING
+             && arg->vval.v_string != NULL
+             && ascii_isdigit(*arg->vval.v_string)) {
+    r = FAIL;
   } else if (arg->v_type == VAR_FUNC || arg->v_type == VAR_STRING) {
     char_u *name = arg->vval.v_string;
     func_ref(name);
@@ -8126,6 +8132,10 @@ bool callback_from_typval(Callback *const callback, typval_T *const arg)
   } else if (arg->v_type == VAR_NUMBER && arg->vval.v_number == 0) {
     callback->type = kCallbackNone;
   } else {
+    r = FAIL;
+  }
+
+  if (r == FAIL) {
     EMSG(_("E921: Invalid callback argument"));
     return false;
   }
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 8c9c326a28..5a27ff21cc 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -2568,7 +2568,7 @@ static bool valid_filetype(const char_u *val)
 bool valid_spellang(const char_u *val)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
-  return valid_name(val, ".-_,");
+  return valid_name(val, ".-_,@");
 }
 
 /// Return true if "val" is a valid 'spellfile' value.
diff --git a/src/nvim/testdir/test_filetype.vim b/src/nvim/testdir/test_filetype.vim
index 7290cceb0b..9605348389 100644
--- a/src/nvim/testdir/test_filetype.vim
+++ b/src/nvim/testdir/test_filetype.vim
@@ -600,6 +600,7 @@ let s:script_checks = {
       \ 'haskell': [['#!/path/haskell']],
       \ 'cpp': [['// Standard iostream objects -*- C++ -*-'],
       \         ['// -*- C++ -*-']],
+      \ 'yaml': [['%YAML 1.2']],
       \ }
 
 func Test_script_detection()
diff --git a/src/nvim/testdir/test_timers.vim b/src/nvim/testdir/test_timers.vim
index 3043103270..40376a877e 100644
--- a/src/nvim/testdir/test_timers.vim
+++ b/src/nvim/testdir/test_timers.vim
@@ -339,4 +339,8 @@ func Test_nocatch_garbage_collect()
   delfunc FeedChar
 endfunc
 
+func Test_timer_invalid_callback()
+  call assert_fails('call timer_start(0, "0")', 'E921')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab