diff --git a/autoload/ale/lsp/message.vim b/autoload/ale/lsp/message.vim
index 1c0499d..9e05156 100644
--- a/autoload/ale/lsp/message.vim
+++ b/autoload/ale/lsp/message.vim
@@ -26,11 +26,13 @@ endfunction
 
 function! ale#lsp#message#Initialize(root_path, initialization_options) abort
     " TODO: Define needed capabilities.
+    " NOTE: rootPath is deprecated in favour of rootUri
     return [0, 'initialize', {
     \   'processId': getpid(),
     \   'rootPath': a:root_path,
     \   'capabilities': {},
     \   'initializationOptions': a:initialization_options,
+    \   'rootUri': ale#path#ToURI(a:root_path),
     \}]
 endfunction
 
diff --git a/test/lsp/test_lsp_client_messages.vader b/test/lsp/test_lsp_client_messages.vader
index e7eda33..dc28c2e 100644
--- a/test/lsp/test_lsp_client_messages.vader
+++ b/test/lsp/test_lsp_client_messages.vader
@@ -17,6 +17,7 @@ Execute(ale#lsp#message#Initialize() should return correct messages):
   \    'rootPath': '/foo/bar',
   \    'capabilities': {},
   \    'initializationOptions': {'foo': 'bar'},
+  \    'rootUri': 'file:///foo/bar',
   \   }
   \ ],
   \ ale#lsp#message#Initialize('/foo/bar', {'foo': 'bar'})