diff --git a/README.mkd b/README.mkd
index add6877..4af6e47 100644
--- a/README.mkd
+++ b/README.mkd
@@ -260,6 +260,7 @@ You can customise:
 * How to handle non-gitgutter signs
 * The signs' colours and symbols
 * Line highlights
+* Whether the diff is relative to the index (default) or working tree.
 * The base of the diff
 * Extra arguments for `git` when running `git diff`
 * Extra arguments for `git diff`
@@ -383,6 +384,15 @@ highlight link GitGutterChangeLineNr Underlined
 ```
 
 
+#### Whether the diff is relative to the index or working tree
+
+By default diffs are relative to the index.  How you can make them relative to the working tree:
+
+```viml
+let g:gitgutter_diff_relative_to = 'working_tree'
+```
+
+
 #### The base of the diff
 
 By default buffers are diffed against the index.  However you can diff against any commit by setting:
@@ -391,6 +401,8 @@ By default buffers are diffed against the index.  However you can diff against a
 let g:gitgutter_diff_base = '<commit SHA>'
 ```
 
+This setting is ignored when the diffs are relative to the working tree.
+
 
 #### Extra arguments for `git` when running `git diff`
 
diff --git a/autoload/gitgutter.vim b/autoload/gitgutter.vim
index 9818871..29b5865 100644
--- a/autoload/gitgutter.vim
+++ b/autoload/gitgutter.vim
@@ -39,7 +39,7 @@ function! gitgutter#process_buffer(bufnr, force) abort
 
       let diff = ''
       try
-        let diff = gitgutter#diff#run_diff(a:bufnr, 'index', 0)
+        let diff = gitgutter#diff#run_diff(a:bufnr, g:gitgutter_diff_relative_to, 0)
       catch /gitgutter not tracked/
         call gitgutter#debug#log('Not tracked: '.gitgutter#utility#file(a:bufnr))
       catch /gitgutter diff failed/
diff --git a/autoload/gitgutter/hunk.vim b/autoload/gitgutter/hunk.vim
index 4bb7aee..16befc9 100644
--- a/autoload/gitgutter/hunk.vim
+++ b/autoload/gitgutter/hunk.vim
@@ -227,7 +227,7 @@ function! s:hunk_op(op, ...)
   if gitgutter#utility#is_active(bufnr)
     " Get a (synchronous) diff.
     let [async, g:gitgutter_async] = [g:gitgutter_async, 0]
-    let diff = gitgutter#diff#run_diff(bufnr, 'index', 1)
+    let diff = gitgutter#diff#run_diff(bufnr, g:gitgutter_diff_relative_to, 1)
     let g:gitgutter_async = async
 
     call gitgutter#hunk#set_hunks(bufnr, gitgutter#diff#parse_diff(diff))
diff --git a/doc/gitgutter.txt b/doc/gitgutter.txt
index 8477828..997e3d1 100644
--- a/doc/gitgutter.txt
+++ b/doc/gitgutter.txt
@@ -276,6 +276,7 @@ Git:~
     |g:gitgutter_git_executable|
     |g:gitgutter_git_args|
     |g:gitgutter_diff_args|
+    |g:gitgutter_diff_relative_to|
     |g:gitgutter_diff_base|
 
 Grep:~
@@ -339,6 +340,15 @@ Use this option to pass any extra arguments to git-diff.  For example:
     let g:gitgutter_diff_args = '-w'
 <
 
+                                                 *g:gitgutter_diff_relative_to*
+Default: empty
+
+By default buffers are diffed against the index.  Use this option to diff against
+the working tree.  For example:
+>
+    let g:gitgutter_diff_relative_to = 'working_tree'
+<
+
                                                         *g:gitgutter_diff_base*
 Default: empty
 
@@ -348,6 +358,10 @@ a revision instead.  For example:
     let g:gitgutter_diff_base = '<some commit SHA>'
 <
 
+This setting is ignore when the diff is relative to the working tree
+(|g:gitgutter_diff_relative_to|).
+
+                                                             *g:gitgutter_grep*
                                                              *g:gitgutter_grep*
 Default: 'grep'
 
diff --git a/plugin/gitgutter.vim b/plugin/gitgutter.vim
index 40124e3..14b413e 100644
--- a/plugin/gitgutter.vim
+++ b/plugin/gitgutter.vim
@@ -54,6 +54,7 @@ endif
 call s:set('g:gitgutter_sign_removed_above_and_below', '[')
 call s:set('g:gitgutter_sign_modified_removed',       '~_')
 call s:set('g:gitgutter_git_args',                      '')
+call s:set('g:gitgutter_diff_relative_to',         'index')
 call s:set('g:gitgutter_diff_args',                     '')
 call s:set('g:gitgutter_diff_base',                     '')
 call s:set('g:gitgutter_map_keys',                       1)