diff --git a/autoload/sy/repo.vim b/autoload/sy/repo.vim
index 8602924..72a32d6 100644
--- a/autoload/sy/repo.vim
+++ b/autoload/sy/repo.vim
@@ -162,13 +162,8 @@ endfunction
 
 " Function: #get_diff_perforce {{{1
 function! sy#repo#get_diff_perforce() abort
-  if has('win32') || has ('win64')
-    let null = 'NUL'
-  else
-    let null = '/dev/null'
-  endif
   let diffoptions = has_key(g:signify_diffoptions, 'perforce') ? g:signify_diffoptions.perforce : ''
-  let diff = system('p4 monitor show 2>&1 >' . null . ' && env P4DIFF=diff p4 diff -dU0 '. diffoptions .' '. sy#util#escape(b:sy.path))
+  let diff = system('p4 monitor show 2>&1 >' . sy#util#devnull() . ' && env P4DIFF=diff p4 diff -dU0 '. diffoptions .' '. sy#util#escape(b:sy.path))
   return v:shell_error ? [0, ''] : [1, diff]
 endfunction
 
diff --git a/autoload/sy/util.vim b/autoload/sy/util.vim
index 402112f..7693c2a 100644
--- a/autoload/sy/util.vim
+++ b/autoload/sy/util.vim
@@ -75,3 +75,13 @@ function! sy#util#hunk_text_object(emptylines) abort
     execute hunks[0].end
   endif
 endfunction
+
+" Function: #devnull {{{1
+function! sy#util#devnull() abort
+  if has('win32') || has ('win64')
+    let null = 'NUL'
+  else
+    let null = '/dev/null'
+  endif
+  return null
+endfunction