diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 213948a028..06ac44e5e4 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -8782,7 +8782,7 @@ void script_host_eval(char *name, typval_T *argvars, typval_T *rettv)
 ///                 an empty typval_T.
 typval_T eval_call_provider(char *provider, char *method, list_T *arguments, bool discard)
 {
-  if (!eval_has_provider(provider)) {
+  if (!eval_has_provider(provider, false)) {
     semsg("E319: No \"%s\" provider found. Run \":checkhealth provider\"",
           provider);
     return (typval_T){
@@ -8840,7 +8840,7 @@ typval_T eval_call_provider(char *provider, char *method, list_T *arguments, boo
 }
 
 /// Checks if provider for feature `feat` is enabled.
-bool eval_has_provider(const char *feat)
+bool eval_has_provider(const char *feat, bool throw_if_fast)
 {
   if (!strequal(feat, "clipboard")
       && !strequal(feat, "python3")
@@ -8853,6 +8853,11 @@ bool eval_has_provider(const char *feat)
     return false;
   }
 
+  if (throw_if_fast && !nlua_is_deferred_safe()) {
+    semsg(e_luv_api_disabled, "Vimscript function");
+    return false;
+  }
+
   char name[32];  // Normalized: "python3_compiled" => "python3".
   snprintf(name, sizeof(name), "%s", feat);
   strchrsub(name, '_', '\0');  // Chop any "_xx" suffix.
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index dcc8cf3c8c..ae42b330a9 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -4905,6 +4905,7 @@ M.funcs = {
       	endif
       <
     ]=],
+    fast = true,
     name = 'has',
     params = { { 'feature', 'any' } },
     returns = '0|1',
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 8e62e3b96f..8528168be1 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -3435,19 +3435,19 @@ static void f_has(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     } else if (STRICMP(name, "syntax_items") == 0) {
       n = syntax_present(curwin);
     } else if (STRICMP(name, "clipboard_working") == 0) {
-      n = eval_has_provider("clipboard");
+      n = eval_has_provider("clipboard", true);
     } else if (STRICMP(name, "pythonx") == 0) {
-      n = eval_has_provider("python3");
+      n = eval_has_provider("python3", true);
     } else if (STRICMP(name, "wsl") == 0) {
       n = has_wsl();
 #ifdef UNIX
     } else if (STRICMP(name, "unnamedplus") == 0) {
-      n = eval_has_provider("clipboard");
+      n = eval_has_provider("clipboard", true);
 #endif
     }
   }
 
-  if (!n && eval_has_provider(name)) {
+  if (!n && eval_has_provider(name, true)) {
     n = true;
   }
 
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 1b103b8aaf..a97c12568d 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -1968,7 +1968,7 @@ static int command_line_handle_key(CommandLineState *s)
     return command_line_not_changed(s);                 // Ignore mouse
 
   case K_MIDDLEMOUSE:
-    cmdline_paste(eval_has_provider("clipboard") ? '*' : 0, true, true);
+    cmdline_paste(eval_has_provider("clipboard", false) ? '*' : 0, true, true);
     redrawcmd();
     return command_line_changed(s);
 
diff --git a/src/nvim/main.c b/src/nvim/main.c
index 50d1a5a735..608684bd36 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -641,7 +641,7 @@ int main(int argc, char **argv)
 
   // WORKAROUND(mhi): #3023
   if (cb_flags & CB_UNNAMEDMASK) {
-    eval_has_provider("clipboard");
+    eval_has_provider("clipboard", false);
   }
 
   if (params.luaf != NULL) {
diff --git a/src/nvim/mouse.c b/src/nvim/mouse.c
index 1e70462700..9d30d7d5ab 100644
--- a/src/nvim/mouse.c
+++ b/src/nvim/mouse.c
@@ -467,7 +467,7 @@ bool do_mouse(oparg_T *oap, int c, int dir, int count, bool fixindent)
       if (regname == '.') {
         insert_reg(regname, true);
       } else {
-        if (regname == 0 && eval_has_provider("clipboard")) {
+        if (regname == 0 && eval_has_provider("clipboard", false)) {
           regname = '*';
         }
         if ((State & REPLACE_FLAG) && !yank_register_mline(regname)) {
@@ -819,7 +819,7 @@ popupexit:
   // Middle mouse click: Put text before cursor.
   if (which_button == MOUSE_MIDDLE) {
     int c2;
-    if (regname == 0 && eval_has_provider("clipboard")) {
+    if (regname == 0 && eval_has_provider("clipboard", false)) {
       regname = '*';
     }
     if (yank_register_mline(regname)) {
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index eba3e98357..b658584410 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -6395,7 +6395,7 @@ static yankreg_T *adjust_clipboard_name(int *name, bool quiet, bool writing)
     goto end;
   }
 
-  if (!eval_has_provider("clipboard")) {
+  if (!eval_has_provider("clipboard", false)) {
     if (batch_change_count <= 1 && !quiet
         && (!clipboard_didwarn || (explicit_cb_reg && !redirecting()))) {
       clipboard_didwarn = true;
diff --git a/test/functional/lua/loop_spec.lua b/test/functional/lua/loop_spec.lua
index d5c5cd3cd0..566a171a84 100644
--- a/test/functional/lua/loop_spec.lua
+++ b/test/functional/lua/loop_spec.lua
@@ -133,6 +133,20 @@ describe('vim.uv', function()
       {5:-- INSERT --}                                      |
     ]])
     eq({ blocking = false, mode = 'n' }, exec_lua('return _G.mode'))
+
+    exec_lua([[
+      local timer = vim.uv.new_timer()
+      timer:start(20, 0, function ()
+        _G.is_fast = vim.in_fast_event()
+        timer:close()
+        _G.value = vim.fn.has("nvim-0.5")
+        _G.unvalue = vim.fn.has("python3")
+      end)
+    ]])
+
+    screen:expect({ any = [[{3:Vim:E5560: Vimscript function must not be called i}]] })
+    feed('<cr>')
+    eq({ 1, nil }, exec_lua('return {_G.value, _G.unvalue}'))
   end)
 
   it("is equal to require('luv')", function()