diff --git a/runtime/lua/vim/lsp/completion.lua b/runtime/lua/vim/lsp/completion.lua
index 729cada68a..0913179af8 100644
--- a/runtime/lua/vim/lsp/completion.lua
+++ b/runtime/lua/vim/lsp/completion.lua
@@ -482,10 +482,7 @@ local function trigger(bufnr, clients, ctx)
   end
 
   local win = api.nvim_get_current_win()
-  local cursor_row, cursor_col = unpack(api.nvim_win_get_cursor(win)) --- @type integer, integer
-  local line = api.nvim_get_current_line()
-  local line_to_cursor = line:sub(1, cursor_col)
-  local word_boundary = vim.fn.match(line_to_cursor, '\\k*$')
+  local cursor_row = api.nvim_win_get_cursor(win)[1]
   local start_time = vim.uv.hrtime() --[[@as integer]]
   Context.last_request_time = start_time
 
@@ -496,13 +493,19 @@ local function trigger(bufnr, clients, ctx)
     Context.pending_requests = {}
     Context.isIncomplete = false
 
-    local row_changed = api.nvim_win_get_cursor(win)[1] ~= cursor_row
+    local new_cursor_row, cursor_col = unpack(api.nvim_win_get_cursor(win)) --- @type integer, integer
+    local row_changed = new_cursor_row ~= cursor_row
     local mode = api.nvim_get_mode().mode
     if row_changed or not (mode == 'i' or mode == 'ic') then
       return
     end
 
-    local matches --[[@type table]] = vim.fn.complete_info({ 'items' })['items']
+    local line = api.nvim_get_current_line()
+    local line_to_cursor = line:sub(1, cursor_col)
+    local word_boundary = vim.fn.match(line_to_cursor, '\\k*$')
+
+    local matches = {}
+
     local server_start_boundary --- @type integer?
     for client_id, response in pairs(responses) do
       local client = lsp.get_client_by_id(client_id)
@@ -530,9 +533,25 @@ local function trigger(bufnr, clients, ctx)
           result,
           encoding
         )
+
         vim.list_extend(matches, client_matches)
       end
     end
+
+    --- @type table[]
+    local prev_matches = vim.fn.complete_info({ 'items', 'matches' })['items']
+
+    --- @param prev_match table
+    prev_matches = vim.tbl_filter(function(prev_match)
+      local client_id = vim.tbl_get(prev_match, 'user_data', 'nvim', 'lsp', 'client_id')
+      if client_id and responses[client_id] ~= nil then
+        return false
+      end
+      return vim.tbl_get(prev_match, 'match')
+    end, prev_matches)
+
+    matches = vim.list_extend(prev_matches, matches)
+
     local start_col = (server_start_boundary or word_boundary) + 1
     Context.cursor = { cursor_row, start_col }
     vim.fn.complete(start_col, matches)
diff --git a/test/functional/plugin/lsp/completion_spec.lua b/test/functional/plugin/lsp/completion_spec.lua
index bb06e40500..dfdfb2533e 100644
--- a/test/functional/plugin/lsp/completion_spec.lua
+++ b/test/functional/plugin/lsp/completion_spec.lua
@@ -810,7 +810,7 @@ end)
 
 --- @param name string
 --- @param completion_result lsp.CompletionList
---- @param opts? {trigger_chars?: string[], resolve_result?: lsp.CompletionItem}
+--- @param opts? {trigger_chars?: string[], resolve_result?: lsp.CompletionItem, delay?: integer}
 --- @return integer
 local function create_server(name, completion_result, opts)
   opts = opts or {}
@@ -824,7 +824,14 @@ local function create_server(name, completion_result, opts)
       },
       handlers = {
         ['textDocument/completion'] = function(_, _, callback)
-          callback(nil, completion_result)
+          if opts.delay then
+            -- simulate delay in completion request, needed for some of these tests
+            vim.defer_fn(function()
+              callback(nil, completion_result)
+            end, opts.delay)
+          else
+            callback(nil, completion_result)
+          end
         end,
         ['completionItem/resolve'] = function(_, _, callback)
           callback(nil, opts.resolve_result)
@@ -1343,3 +1350,49 @@ describe('vim.lsp.completion: integration', function()
     )
   end)
 end)
+
+describe("vim.lsp.completion: omnifunc + 'autocomplete'", function()
+  before_each(function()
+    clear()
+    exec_lua(create_server_definition)
+    exec_lua(function()
+      -- enable buffer and omnifunc autocompletion
+      -- omnifunc will be the lsp omnifunc
+      vim.o.complete = '.,o'
+      vim.o.autocomplete = true
+    end)
+
+    local completion_list = {
+      isIncomplete = false,
+      items = {
+        { label = 'hello' },
+        { label = 'hallo' },
+      },
+    }
+    create_server('dummy', completion_list, { delay = 50 })
+  end)
+
+  local function assert_matches(expected)
+    retry(nil, nil, function()
+      local matches = vim.tbl_map(function(m)
+        return m.word
+      end, exec_lua('return vim.fn.complete_info({ "items" })').items)
+      eq(expected, matches)
+    end)
+  end
+
+  it('merges with other completions', function()
+    feed('ihillo<cr><esc>ih')
+    assert_matches({ 'hillo', 'hallo', 'hello' })
+  end)
+
+  it('fuzzy matches without duplication', function()
+    -- wait for one completion request to start and then request another before
+    -- the first one finishes, then wait for both to finish
+    feed('ihillo<cr>h')
+    vim.uv.sleep(1)
+    feed('e')
+
+    assert_matches({ 'hello' })
+  end)
+end)