diff --git a/autoload/vundle.vim b/autoload/vundle.vim
index dded571d..0b784d53 100644
--- a/autoload/vundle.vim
+++ b/autoload/vundle.vim
@@ -61,6 +61,20 @@ endif
 " :Plugin command in the vimrc.  It is not possible to do this automatically
 " because when loading the vimrc file no plugins where loaded yet.
 func! vundle#rc(...) abort
+  " If this function has already been called and Vim hasn't finished loading,
+  " that is, we are not sourcing our .vimrc file later on, Vundle is probably
+  " loading from several sources which can lead to unpredictable results.
+  if exists('g:vundle_loading') && g:vundle_loading
+    echoerr 'Vundle is probably loading from several sources. ' .
+          \ 'This can lead to unpredictable results! ' .
+          \ 'Please find and remove the duplication.'
+  endif
+
+  " Set g:vundle_loading only if Vim hasn't finished loading.
+  if !exists('g:vundle_loaded') || !g:vundle_loaded
+    let g:vundle_loading = 1
+  endif
+
   let g:bundle_dir = len(a:000) > 0 ? expand(a:1, 1) : expand('$HOME/.vim/bundle', 1)
   let g:updated_bundles = []
   let g:vundle_log = []
@@ -81,4 +95,12 @@ func! vundle#end(...) abort
   call vundle#config#activate_bundles()
 endf
 
+augroup vundle
+  au!
+
+  " Tell Vundle it has finished loading and Vim is up and running.
+  au VimEnter * unlet g:vundle_loading
+  au VimEnter * let g:vundle_loaded = 1
+augroup END
+
 " vim: set expandtab sts=2 ts=2 sw=2 tw=78 norl: