diff --git a/autoload/fugitive.vim b/autoload/fugitive.vim
index 081dfa7..99b643e 100644
--- a/autoload/fugitive.vim
+++ b/autoload/fugitive.vim
@@ -634,7 +634,7 @@ function! s:buffer(...) abort
   if buffer.getvar('git_dir') !=# ''
     return buffer
   endif
-  call s:throw('not a git repository: '.expand('%:p'))
+  call s:throw('not a git repository: '.bufname(buffer['#']))
 endfunction
 
 function! fugitive#buffer(...) abort
@@ -1239,7 +1239,14 @@ function! s:Commit(mods, args, ...) abort
         let args = a:args
         let args = s:gsub(args,'%(%(^| )-- )@<!%(^| )@<=%(-[esp]|--edit|--interactive|--patch|--signoff)%($| )','')
         let args = s:gsub(args,'%(%(^| )-- )@<!%(^| )@<=%(-c|--reedit-message|--reuse-message|-F|--file|-m|--message)%(\s+|\=)%(''[^'']*''|"%(\\.|[^"])*"|\\.|\S)*','')
-        let args = s:gsub(args,'%(^| )@<=[%#]%(:\w)*','\=expand(submatch(0))')
+        let cd = exists('*haslocaldir') && haslocaldir() ? 'lcd' : 'cd'
+        let cwd = getcwd()
+        try
+          exe cd s:fnameescape(repo.tree())
+          let args = s:gsub(args,'\\@<!(\%|##=|#\<=\d+)(:\w)*','\=fnamemodify(FugitivePath(expand(submatch(1))),":." . submatch(2))')
+        finally
+          exe cd cwd
+        endtry
         let args = s:sub(args, '\ze -- |$', ' --no-edit --no-interactive --no-signoff')
         let args = '-F '.s:shellesc(msgfile).' '.args
         if args !~# '\%(^\| \)--cleanup\>'