diff --git a/plugin/showmarks.vim b/plugin/showmarks.vim
index affd240..90f9c59 100644
--- a/plugin/showmarks.vim
+++ b/plugin/showmarks.vim
@@ -514,7 +514,7 @@ if !isdirectory(docdir)
   unlet docdir
   finish
  elseif !has("mac")
-  exe "!mkdir ".docdir
+  exe '!mkdir "'.docdir.'"'
  endif
 endif