diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 533fa95e99..03ab2a76ad 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -1593,6 +1593,10 @@ static void init_prompt(int cmdchar_todo)
   char *prompt = prompt_text();
   int prompt_len = (int)strlen(prompt);
 
+  // In case the mark is set to a nonexistent line.
+  curbuf->b_prompt_start.mark.lnum = MIN(curbuf->b_prompt_start.mark.lnum,
+                                         curbuf->b_ml.ml_line_count);
+
   curwin->w_cursor.lnum = MAX(curwin->w_cursor.lnum, curbuf->b_prompt_start.mark.lnum);
   char *text = ml_get(curbuf->b_prompt_start.mark.lnum);
   colnr_T text_len = ml_get_len(curbuf->b_prompt_start.mark.lnum);
diff --git a/test/functional/legacy/prompt_buffer_spec.lua b/test/functional/legacy/prompt_buffer_spec.lua
index 1acc6a2258..2b2f73f5dc 100644
--- a/test/functional/legacy/prompt_buffer_spec.lua
+++ b/test/functional/legacy/prompt_buffer_spec.lua
@@ -671,6 +671,13 @@ describe('prompt buffer', function()
     -- No crash from invalid col.
     eq(true, api.nvim_buf_set_mark(0, ':', fn('line', '.'), 999, {}))
     eq({ 12, 6 }, api.nvim_buf_get_mark(0, ':'))
+
+    -- No ml_get error from invalid lnum.
+    command('set messagesopt+=wait:0 messagesopt-=hit-enter')
+    fn('setpos', "':", { 0, 999, 7, 0 })
+    eq('', api.nvim_get_vvar('errmsg'))
+    command('set messagesopt&')
+    eq({ 12, 6 }, api.nvim_buf_get_mark(0, ':'))
   end)
 
   describe('prompt_getinput', function()