diff --git a/README.md b/README.md
index bcdc6289..74a113de 100644
--- a/README.md
+++ b/README.md
@@ -350,7 +350,19 @@ and display any new diagnostics it encounters. Do note that recompilation with
 this command may take a while and during this time the Vim GUI _will_ be
 blocked.
 
-TODO: extending the semantic engine for other langs, using ListToggle
+After the errors are displayed by Syntastic, it will display a short diagnostic
+message when you move your cursor to the line with the error. You can get a
+detailed diagnostic message with the `<leader>d` key mapping (can be changed in
+the options) YCM provides when your cursor is on the line with the diagnostic.
+
+You can also see the full diagnostic message for all the diagnostics in the
+current file in Vim's `locationlist`, which can be opened with the `:lopen` and
+`:lclose` commands. A good way to toggle the display of the `locationlist` with
+a single key mapping is provided by another (very small) Vim plugin called
+[ListToggle][] (which also makes it possible to change the height of the
+`locationlist` window), also written by yours truly.
+
+TODO: extending the semantic engine for other langs
 
 Options
 -------
@@ -510,11 +522,19 @@ default mapping will probably only work in GUI Vim (Gvim or MacVim) and not in
 plain console Vim because the terminal usually does not forward modifier key
 combinations to Vim.
 
-
 Default: `<C-Space>`
 
     let g:ycm_key_invoke_completion = '<C-Space>'
 
+### The `g:ycm_key_detailed_diagnostics` option
+
+This option controls the key mapping used to show the full diagnostic text when
+the user's cursor is on the line with the diagnostic.
+
+Default: `<leader>d`
+
+    let g:ycm_key_detailed_diagnostics = '<leader>d'
+
 ### The `g:ycm_global_ycm_extra_conf` option
 
 Normally, YCM searches for a `.ycm_extra_conf.py` file for compilation flags
@@ -603,3 +623,4 @@ This software is licensed under the [GPL v3 license][gpl].
 [flags_example]: https://github.com/Valloric/YouCompleteMe/blob/master/cpp/ycm/.ycm_extra_conf.py
 [compdb]: http://clang.llvm.org/docs/JSONCompilationDatabase.html
 [subsequence]: http://en.wikipedia.org/wiki/Subsequence
+[listtoggle]: https://github.com/Valloric/ListToggle
diff --git a/autoload/youcompleteme.vim b/autoload/youcompleteme.vim
index 45f28140..babc46b2 100644
--- a/autoload/youcompleteme.vim
+++ b/autoload/youcompleteme.vim
@@ -72,8 +72,8 @@ function! youcompleteme#Enable()
   " candidate that vim selects by default
   exe 'inoremap <unique> ' . g:ycm_key_invoke_completion . ' <C-X><C-O><C-P>'
 
-  " TODO: make this a nicer, customizable map
-  nnoremap <unique> <leader>d :call <sid>ShowDetailedDiagnostic()<cr>
+  exe 'nnoremap <unique> ' . g:ycm_key_detailed_diagnostics .
+        \ ' :call <sid>ShowDetailedDiagnostic()<cr>'
 
   py import sys
   py import vim
diff --git a/plugin/youcompleteme.vim b/plugin/youcompleteme.vim
index 2a3b4446..43acc035 100644
--- a/plugin/youcompleteme.vim
+++ b/plugin/youcompleteme.vim
@@ -85,6 +85,9 @@ let g:ycm_key_previous_completion =
 let g:ycm_key_invoke_completion =
       \ get( g:, 'ycm_key_invoke_completion', '<C-Space>' )
 
+let g:ycm_key_detailed_diagnostics =
+      \ get( g:, 'ycm_key_detailed_diagnostics', '<leader>d' )
+
 let g:ycm_global_ycm_extra_conf =
       \ get( g:, 'ycm_global_ycm_extra_conf', '' )