diff --git a/lua/codecompanion/init.lua b/lua/codecompanion/init.lua
index b9186223..6c960d64 100644
--- a/lua/codecompanion/init.lua
+++ b/lua/codecompanion/init.lua
@@ -1,3 +1,4 @@
+local buf_utils = require("codecompanion.utils.buffers")
 local config = require("codecompanion.config")
 local context_utils = require("codecompanion.utils.context")
 local log = require("codecompanion.utils.log")
@@ -265,26 +266,31 @@ M.setup = function(opts)
   local group = "codecompanion.syntax"
   api.nvim_create_augroup(group, { clear = true })
   api.nvim_create_autocmd("FileType", {
-    pattern = "codecompanion",
+    pattern = "markdown",
     group = group,
-    callback = vim.schedule_wrap(function()
-      vim.iter(config.strategies.chat.variables):each(function(name, var)
-        vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. '"')
-        if var.opts and var.opts.has_params then
-          vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. ':\\d\\+-\\?\\d\\+"')
-        end
-      end)
-      vim.iter(config.strategies.agent.tools):each(function(name, _)
-        vim.cmd.syntax('match CodeCompanionChatTool "@' .. name .. '"')
-      end)
-      vim
-        .iter(config.strategies.agent)
-        :filter(function(name)
-          return name ~= "tools"
+    callback = vim.schedule_wrap(function(info)
+      if not api.nvim_buf_is_valid(info.buf) or not buf_utils.is_codecompanion_buffer(info.buf) then
+        return
+      end
+      api.nvim_buf_call(info.buf, function()
+        vim.iter(config.strategies.chat.variables):each(function(name, var)
+          vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. '"')
+          if var.opts and var.opts.has_params then
+            vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. ':\\d\\+-\\?\\d\\+"')
+          end
         end)
-        :each(function(name, _)
-          vim.cmd.syntax('match CodeCompanionChatAgent "@' .. name .. '"')
+        vim.iter(config.strategies.agent.tools):each(function(name, _)
+          vim.cmd.syntax('match CodeCompanionChatTool "@' .. name .. '"')
         end)
+        vim
+          .iter(config.strategies.agent)
+          :filter(function(name)
+            return name ~= "tools"
+          end)
+          :each(function(name, _)
+            vim.cmd.syntax('match CodeCompanionChatAgent "@' .. name .. '"')
+          end)
+      end)
     end),
   })
 
@@ -334,26 +340,35 @@ M.setup = function(opts)
     cmp.register_source("codecompanion_slash_commands", require(completion .. ".slash_commands").new(config))
     cmp.register_source("codecompanion_tools", require(completion .. ".tools").new(config))
     cmp.register_source("codecompanion_variables", require(completion .. ".variables").new())
-    cmp.setup.filetype("codecompanion", {
+    cmp.setup.filetype("markdown", {
       enabled = true,
-      sources = {
+      sources = vim.list_extend({
         { name = "codecompanion_models" },
         { name = "codecompanion_slash_commands" },
         { name = "codecompanion_tools" },
         { name = "codecompanion_variables" },
-      },
+      }, cmp.get_config().sources),
     })
   end
 
   -- Capture the last terminal buffer
   _G.codecompanion_last_terminal = nil
+
+  ---Check if given buffer is a terminal buffer
+  ---and set `_G.codecompanion_last_terminal` if it is
+  ---@param buf number? when nil, the current buffer is used
+  local function check_terminal(buf)
+    local buf = buf ~= 0 and buf or api.nvim_get_current_buf()
+    if vim.api.nvim_buf_is_valid(buf) and vim.bo[buf].buftype == "terminal" then
+      _G.codecompanion_last_terminal = buf
+    end
+  end
+
+  check_terminal()
   api.nvim_create_autocmd("TermEnter", {
     desc = "Capture the last terminal buffer",
-    callback = function()
-      local bufnr = api.nvim_get_current_buf()
-      if vim.bo[bufnr].buftype == "terminal" then
-        _G.codecompanion_last_terminal = bufnr
-      end
+    callback = function(info)
+      check_terminal(info.buf)
     end,
   })
 
diff --git a/lua/codecompanion/keymaps.lua b/lua/codecompanion/keymaps.lua
index 7ad7f460..8f6425b3 100644
--- a/lua/codecompanion/keymaps.lua
+++ b/lua/codecompanion/keymaps.lua
@@ -4,6 +4,7 @@ local config = require("codecompanion.config")
 local async = require("plenary.async")
 local ts = require("codecompanion.utils.treesitter")
 local ui = require("codecompanion.utils.ui")
+local buf = require("codecompanion.utils.buffers")
 local util = require("codecompanion.utils")
 
 local api = vim.api
@@ -33,7 +34,7 @@ local function open_float(lines, opts)
   local height = window.height > 1 and window.height or opts.height or 17
 
   local bufnr = api.nvim_create_buf(false, true)
-  util.set_option(bufnr, "filetype", opts.filetype or "codecompanion")
+  buf.set_codecompanion_buffer(bufnr)
   local winnr = api.nvim_open_win(bufnr, true, {
     relative = opts.relative or "cursor",
     border = "single",
diff --git a/lua/codecompanion/providers/completion/blink/init.lua b/lua/codecompanion/providers/completion/blink/init.lua
index dd0a67e6..b1d208e0 100644
--- a/lua/codecompanion/providers/completion/blink/init.lua
+++ b/lua/codecompanion/providers/completion/blink/init.lua
@@ -1,4 +1,5 @@
 local completion = require("codecompanion.completion")
+local buf = require("codecompanion.utils.buffers")
 
 local slash_commands = completion.slash_commands()
 local tools = completion.tools()
@@ -15,7 +16,7 @@ function M:get_trigger_characters()
 end
 
 function M:enabled()
-  return vim.bo.filetype == "codecompanion"
+  return buf.is_codecompanion_buffer()
 end
 
 function M:get_completions(ctx, callback)
diff --git a/lua/codecompanion/providers/completion/cmp/models.lua b/lua/codecompanion/providers/completion/cmp/models.lua
index b662d186..c14a40cb 100644
--- a/lua/codecompanion/providers/completion/cmp/models.lua
+++ b/lua/codecompanion/providers/completion/cmp/models.lua
@@ -1,3 +1,5 @@
+local buf = require("codecompanion.utils.buffers")
+
 local source = {}
 
 ---@param config table
@@ -8,7 +10,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion" and self.config.display.chat.show_settings
+  return buf.is_codecompanion_buffer() and self.config.display.chat.show_settings
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/providers/completion/cmp/slash_commands.lua b/lua/codecompanion/providers/completion/cmp/slash_commands.lua
index f3608a34..4b7eeb5c 100644
--- a/lua/codecompanion/providers/completion/cmp/slash_commands.lua
+++ b/lua/codecompanion/providers/completion/cmp/slash_commands.lua
@@ -1,4 +1,5 @@
 local SlashCommands = require("codecompanion.strategies.chat.slash_commands")
+local buf = require("codecompanion.utils.buffers")
 local completion = require("codecompanion.completion")
 local strategy = require("codecompanion.strategies")
 
@@ -9,7 +10,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return buf.is_codecompanion_buffer()
 end
 
 function source:get_trigger_characters()
diff --git a/lua/codecompanion/providers/completion/cmp/tools.lua b/lua/codecompanion/providers/completion/cmp/tools.lua
index d793224c..b56f1def 100644
--- a/lua/codecompanion/providers/completion/cmp/tools.lua
+++ b/lua/codecompanion/providers/completion/cmp/tools.lua
@@ -1,3 +1,5 @@
+local buf = require("codecompanion.utils.buffers")
+
 local source = {}
 
 function source.new(config)
@@ -5,7 +7,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return buf.is_codecompanion_buffer()
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/providers/completion/cmp/variables.lua b/lua/codecompanion/providers/completion/cmp/variables.lua
index fdc2cb7a..21ebb6b9 100644
--- a/lua/codecompanion/providers/completion/cmp/variables.lua
+++ b/lua/codecompanion/providers/completion/cmp/variables.lua
@@ -1,3 +1,5 @@
+local buf = require("codecompanion.utils.buffers")
+
 local source = {}
 
 function source.new()
@@ -5,7 +7,7 @@ function source.new()
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return buf.is_codecompanion_buffer()
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/strategies/chat/init.lua b/lua/codecompanion/strategies/chat/init.lua
index 210146ae..f5ca18ca 100644
--- a/lua/codecompanion/strategies/chat/init.lua
+++ b/lua/codecompanion/strategies/chat/init.lua
@@ -9,6 +9,7 @@ local keymaps = require("codecompanion.utils.keymaps")
 local log = require("codecompanion.utils.log")
 local util = require("codecompanion.utils")
 local yaml = require("codecompanion.utils.yaml")
+local buf = require("codecompanion.utils.buffers")
 
 local api = vim.api
 
@@ -227,7 +228,7 @@ function Chat.new(args)
     create_buf = function()
       local bufnr = api.nvim_create_buf(false, true)
       api.nvim_buf_set_name(bufnr, string.format("[CodeCompanion] %d", id))
-      vim.bo[bufnr].filetype = "codecompanion"
+      buf.set_codecompanion_buffer(bufnr)
 
       return bufnr
     end,
diff --git a/lua/codecompanion/utils/buffers.lua b/lua/codecompanion/utils/buffers.lua
index 2925e13f..31ba537b 100644
--- a/lua/codecompanion/utils/buffers.lua
+++ b/lua/codecompanion/utils/buffers.lua
@@ -11,7 +11,7 @@ function M.get_visible_lines()
   for _, win in ipairs(wins) do
     local bufnr = vim.api.nvim_win_get_buf(win)
 
-    if vim.api.nvim_get_option_value("filetype", { buf = bufnr }) ~= "codecompanion" then
+    if not buf.is_codecompanion_buffer(bufnr) then
       local start_line = vim.api.nvim_win_call(win, function()
         return vim.fn.line("w0")
       end)
@@ -145,4 +145,23 @@ function M.format(bufnr, range)
   )
 end
 
+---Check if a buffer is a codecompanion buffer
+---@param bufnr integer? default to current buffer
+---@return boolean?
+function M.is_codecompanion_buffer(bufnr)
+  return vim.b[bufnr or 0].codecompanion
+end
+
+---Set filetype and buffer-local variable to mark a buffer as a codecompanion
+---buffer
+---
+---Notice that we first set the buffer-local variable and then the filetype so
+---that user can set autocmds on `FileType` event and check if the buffer is a
+---codecompanion buffer by checking `vim.b.codecompanion` variable
+---@param bufnr integer? default to current buffer
+function M.set_codecompanion_buffer(bufnr)
+  vim.b[bufnr or 0].codecompanion = true
+  vim.bo[bufnr or 0].filetype = "markdown"
+end
+
 return M
diff --git a/lua/legendary/extensions/codecompanion.lua b/lua/legendary/extensions/codecompanion.lua
index b96ff092..ceb2a31f 100644
--- a/lua/legendary/extensions/codecompanion.lua
+++ b/lua/legendary/extensions/codecompanion.lua
@@ -1,10 +1,16 @@
+local buf = require("codecompanion.utils.buffers")
+
 local function to_legendary_keymap(key, keymap)
   return {
     key,
     -- prefix makes it easier to search in legendary.nvim window
     desc = string.format("CodeCompanion: %s", require("legendary.util").get_desc(keymap)),
     -- keymaps are all for the chat buffer
-    filters = { filetype = "codecompanion" },
+    filters = {
+      function(_, context)
+        return buf.is_codecompanion_buffer(context.buf)
+      end,
+    },
   }
 end