diff --git a/README.md b/README.md
index c8919c1..2df8045 100644
--- a/README.md
+++ b/README.md
@@ -104,23 +104,14 @@ If you want to use a key that's already used for completion purposes, take a loo
 local cmp = require('cmp')
 local neogen = require('neogen')
 
-local t = function(str)
-    return vim.api.nvim_replace_termcodes(str, true, true, true)
-end
-
-local check_back_space = function()
-    local col = vim.fn.col '.' - 1
-    return col == 0 or vim.fn.getline('.'):sub(col, col):match '%s' ~= nil
-end
-
 cmp.setup {
     ...
 
     -- You must set mapping if you want.
     mapping = {
         ["<tab>"] = cmp.mapping(function(fallback)
-            if neogen.jumpable() then
-                vim.fn.feedkeys(t("<cmd>lua require('neogen').jump_next()<CR>"), "")
+            if require('neogen').jumpable() then
+                require('neogen').jump_next()
             else
                 fallback()
             end
@@ -129,8 +120,8 @@ cmp.setup {
             "s",
         }),
         ["<S-tab>"] = cmp.mapping(function(fallback)
-            if neogen.jumpable(-1) then
-                vim.fn.feedkeys(t("<cmd>lua require('neogen').jump_prev()<CR>"), "")
+            if require('neogen').jumpable(true) then
+                require('neogen').jump_prev()
             else
                 fallback()
             end
diff --git a/lua/neogen/mark.lua b/lua/neogen/mark.lua
index 45d9a07..3a5f7d2 100644
--- a/lua/neogen/mark.lua
+++ b/lua/neogen/mark.lua
@@ -34,11 +34,14 @@ mark.mark_len = function(self)
 end
 
 mark.jumpable = function(self, reverse)
+    if not self.started then
+        return false
+    end
     local ret = true
     if reverse then
-        ret = self.index ~= 1
+        ret = self.index > 0
     else
-        ret = #self.ids ~= self.index
+        ret = #self.ids >= self.index
     end
     if ret then
         ret = self.bufnr == api.nvim_get_current_buf() and self.winid == api.nvim_get_current_win()
@@ -47,10 +50,14 @@ mark.jumpable = function(self, reverse)
 end
 
 mark.jump = function(self, reverse)
-    if self.index == 0 or mark:jumpable(reverse) then
+    if mark:jumpable(reverse) then
         self.index = reverse and self.index - 1 or self.index + 1
-        local line, row = unpack(self:get_mark(self.index))
-        api.nvim_win_set_cursor(self.winid, {line + 1, row})
+        if self.index > 0 and self.index <= #self.ids then
+            local line, row = unpack(self:get_mark(self.index))
+            api.nvim_win_set_cursor(self.winid, {line + 1, row})
+        else
+            self:stop(true)
+        end
     else
         self:stop(true)
     end