diff --git a/runtime/lua/vim/lsp/client.lua b/runtime/lua/vim/lsp/client.lua
index b256eab1a6..1dc8c18a85 100644
--- a/runtime/lua/vim/lsp/client.lua
+++ b/runtime/lua/vim/lsp/client.lua
@@ -678,6 +678,12 @@ function Client:request(method, params, handler, bufnr)
   bufnr = vim._resolve_bufnr(bufnr)
   local version = lsp.util.buf_versions[bufnr]
   log.debug(self._log_prefix, 'client.request', self.id, method, params, handler, bufnr)
+
+  -- Detect if request resolved synchronously (only possible with in-process servers).
+  local already_responded = false
+  local request_registered = false
+
+  -- NOTE: rpc.request might call an in-process (Lua) server, thus may be synchronous.
   local success, request_id = self.rpc.request(method, params, function(err, result)
     handler(err, result, {
       method = method,
@@ -688,11 +694,15 @@ function Client:request(method, params, handler, bufnr)
     })
   end, function(request_id)
     -- Called when the server sends a response to the request (including cancelled acknowledgment).
-    self:_process_request(request_id, 'complete')
+    if request_registered then
+      self:_process_request(request_id, 'complete')
+    end
+    already_responded = true
   end)
 
-  if success and request_id then
+  if success and request_id and not already_responded then
     self:_process_request(request_id, 'pending', bufnr, method)
+    request_registered = true
   end
 
   return success, request_id
diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index 3257a7bfbb..dedf2472c3 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -1252,6 +1252,67 @@ describe('LSP', function()
       }
     end)
 
+    it('request should not be pending for sync responses (in-process LS)', function()
+      clear()
+
+      --- @type boolean
+      local pending_request = exec_lua(function()
+        local function server(dispatchers)
+          local closing = false
+          local srv = {}
+          local request_id = 0
+
+          function srv.request(method, _params, callback, notify_reply_callback)
+            if method == 'textDocument/formatting' then
+              callback(nil, {})
+            elseif method == 'initialize' then
+              callback(nil, {
+                capabilities = {
+                  textDocument = {
+                    formatting = true,
+                  },
+                },
+              })
+            elseif method == 'shutdown' then
+              callback(nil, nil)
+            end
+            request_id = request_id + 1
+            if notify_reply_callback then
+              notify_reply_callback(request_id)
+            end
+            return true, request_id
+          end
+
+          function srv.notify(method)
+            if method == 'exit' then
+              dispatchers.on_exit(0, 15)
+            end
+          end
+          function srv.is_closing()
+            return closing
+          end
+          function srv.terminate()
+            closing = true
+          end
+
+          return srv
+        end
+
+        local client_id = assert(vim.lsp.start({ cmd = server }))
+        local client = assert(vim.lsp.get_client_by_id(client_id))
+
+        local ok, request_id = client:request('textDocument/formatting', {})
+        assert(ok)
+
+        local has_pending = client.requests[request_id] ~= nil
+        vim.lsp.stop_client(client_id)
+
+        return has_pending
+      end)
+
+      eq(false, pending_request, 'expected no pending requests')
+    end)
+
     it('should trigger LspRequest autocmd when requests table changes', function()
       local expected_handlers = {
         { NIL, {}, { method = 'finish', client_id = 1 } },