diff --git a/autoload/vsnip_integ/integration/vimlsp.vim b/autoload/vsnip_integ/integration/vimlsp.vim
index 5e5c3c0..d068ac6 100644
--- a/autoload/vsnip_integ/integration/vimlsp.vim
+++ b/autoload/vsnip_integ/integration/vimlsp.vim
@@ -3,7 +3,11 @@
 "
 function! vsnip_integ#integration#vimlsp#attach() abort
   let g:lsp_text_edit_enabled = v:true
+
+  " save existing value because it may be user-defined.
+  let s:existing_capabilities_function = get(g:, lsp_get_supported_capabilities)
   let g:lsp_get_supported_capabilities = [function('s:get_supported_capabilities')]
+
   let g:lsp_snippet_expand = [{ option -> vsnip#anonymous(option.snippet) }]
 endfunction
 
@@ -11,7 +15,7 @@ endfunction
 " get_supported_capabilities.
 "
 function! s:get_supported_capabilities(server_info) abort
-  let l:capabilities = lsp#default_get_supported_capabilities(a:server_info)
+  let l:capabilities = call(s:existing_capabilities_function[0], [a:server_info])
 
   if !has_key(l:capabilities, 'textDocument')
     let l:capabilities.textDocument = {}