diff --git a/autoload/airline/extensions/branch.vim b/autoload/airline/extensions/branch.vim
index 738ec3f..e589d23 100644
--- a/autoload/airline/extensions/branch.vim
+++ b/autoload/airline/extensions/branch.vim
@@ -3,13 +3,18 @@
 
 scriptencoding utf-8
 
-let s:has_fugitive = exists('*fugitive#head')
-let s:has_lawrencium = exists('*lawrencium#statusline')
-let s:has_vcscommand = get(g:, 'airline#extensions#branch#use_vcscommand', 0) && exists('*VCSCommandGetStatusLine')
-
-if !s:has_fugitive && !s:has_lawrencium && !s:has_vcscommand
-  finish
-endif
+function! s:has_fugitive()
+  return exists('*fugitive#head')
+endfunction
+function! s:has_lawrencium()
+  return exists('*lawrencium#statusline')
+endfunction
+function! s:has_vcscommand()
+  return get(g:, 'airline#extensions#branch#use_vcscommand', 0) && exists('*VCSCommandGetStatusLine')
+endfunction
+function! s:has_custom_scm()
+  return !empty(get(g:, 'airline#extensions#branch#custom_head', ''))
+endfunction
 
 " s:vcs_config contains static configuration of VCSes and their status relative
 " to the active file.
@@ -89,7 +94,7 @@ let s:names = {'0': 'index', '1': 'orig', '2':'fetch', '3':'merge'}
 let s:sha1size = get(g:, 'airline#extensions#branch#sha1_len', 7)
 
 function! s:update_git_branch()
-  if !s:has_fugitive
+  if !s:has_fugitive()
     let s:vcs_config['git'].branch = ''
     return
   endif
@@ -123,7 +128,7 @@ function! s:display_git_branch()
 endfunction
 
 function! s:update_hg_branch()
-  if s:has_lawrencium
+  if s:has_lawrencium()
     let cmd='LC_ALL=C hg qtop'
     let stl=lawrencium#statusline()
     let file=expand('%:p')
@@ -248,7 +253,7 @@ function! airline#extensions#branch#head()
   endfor
 
   if empty(heads)
-    if s:has_vcscommand
+    if s:has_vcscommand()
       call VCSCommandEnableBufferSetup()
       if exists('b:VCSCommandBufferInfo')
         let b:airline_head = s:format_name(get(b:VCSCommandBufferInfo, 0, ''))
@@ -256,6 +261,15 @@ function! airline#extensions#branch#head()
     endif
   endif
 
+  if empty(heads)
+    if s:has_custom_scm()
+      try
+        let Fn = function(g:airline#extensions#branch#custom_head)
+        let b:airline_head = Fn()
+      endtry
+    endif
+  endif
+
   if exists("g:airline#extensions#branch#displayed_head_limit")
     let w:displayed_head_limit = g:airline#extensions#branch#displayed_head_limit
     if len(b:airline_head) > w:displayed_head_limit - 1
diff --git a/doc/airline.txt b/doc/airline.txt
index 72f2713..abf9528 100644
--- a/doc/airline.txt
+++ b/doc/airline.txt
@@ -465,6 +465,23 @@ notexists symbol will be displayed after the branch name.
 <
 * truncate sha1 commits at this number of characters  >
   let g:airline#extensions#branch#sha1_len = 10
+
+* customize branch name retrieval for any version control system >
+  let g:airline#extensions#branch#custom_head = 'GetScmBranch'
+  function! GetScmBranch()
+    if !exists('b:perforce_client')
+      let b:perforce_client = system('p4 client -o | grep Client')
+      " Invalidate cache to prevent stale data when switching clients. Use a
+      " buffer-unique group name to prevent clearing autocmds for other
+      " buffers.
+      exec 'augroup perforce_client-'. bufnr("%")
+          au!
+          autocmd BufWinLeave <buffer> silent! unlet! b:perforce_client
+      augroup END
+    endif
+    return b:perforce_client
+  endfunction
+
 <
 -------------------------------------                    *airline-syntastic*
 syntastic <https://github.com/vim-syntastic/syntastic>