diff --git a/runtime/lua/vim/lsp/client.lua b/runtime/lua/vim/lsp/client.lua
index 5b3ea2ae25..66bf09f231 100644
--- a/runtime/lua/vim/lsp/client.lua
+++ b/runtime/lua/vim/lsp/client.lua
@@ -1436,6 +1436,8 @@ function Client:_on_detach(bufnr)
     end
   end
 
+  vim.diagnostic.reset(vim.lsp.diagnostic.get_namespace(self.id, false), bufnr)
+
   changetracking.reset_buf(self, bufnr)
 
   self:_text_document_did_close_handler(bufnr)
diff --git a/test/functional/plugin/lsp/diagnostic_spec.lua b/test/functional/plugin/lsp/diagnostic_spec.lua
index 5481638bf2..1edc4a7e2b 100644
--- a/test/functional/plugin/lsp/diagnostic_spec.lua
+++ b/test/functional/plugin/lsp/diagnostic_spec.lua
@@ -103,26 +103,26 @@ describe('vim.lsp.diagnostic', function()
 
   describe('vim.lsp.diagnostic.on_publish_diagnostics', function()
     before_each(function()
+      exec_lua(create_server_definition)
       exec_lua(function()
-        client_id = assert(vim.lsp.start({
-          cmd_env = {
-            NVIM_LUA_NOTRACK = '1',
+        _G.requests = 0
+        _G.server = _G._create_server({
+          capabilities = {
+            diagnosticProvider = {},
           },
-          cmd = {
-            vim.v.progpath,
-            '-es',
-            '-u',
-            'NONE',
-            '--headless',
-          },
-          offset_encoding = 'utf-16',
-        }, { attach = false }))
+        })
+
+        client_id = assert(vim.lsp.start({ name = 'dummy', cmd = _G.server.cmd }))
       end)
     end)
 
     after_each(function()
       exec_lua(function()
-        vim.lsp.get_client_by_id(client_id):stop()
+        local client = vim.lsp.get_client_by_id(client_id)
+        if client then
+          client:stop()
+        end
+
         vim.api.nvim_exec_autocmds('VimLeavePre', { modeline = false })
       end)
     end)
@@ -269,6 +269,37 @@ describe('vim.lsp.diagnostic', function()
       eq(1, #before_delete)
       eq(0, #after_delete)
     end)
+
+    it('clears diagnostics when client is detached', function()
+      exec_lua(function()
+        vim.lsp.diagnostic.on_publish_diagnostics(nil, {
+          uri = fake_uri,
+          diagnostics = {
+            _G.make_error('Diagnostic', 0, 0, 0, 0),
+          },
+        }, { client_id = client_id })
+      end)
+
+      eq(
+        1,
+        exec_lua(function()
+          local ns = vim.lsp.diagnostic.get_namespace(client_id)
+          return #vim.diagnostic.get(diagnostic_bufnr, { namespace = ns })
+        end)
+      )
+
+      exec_lua(function()
+        vim.lsp.get_client_by_id(client_id):stop()
+      end)
+
+      eq(
+        0,
+        exec_lua(function()
+          local ns = vim.lsp.diagnostic.get_namespace(client_id)
+          return #vim.diagnostic.get(diagnostic_bufnr, { namespace = ns })
+        end)
+      )
+    end)
   end)
 
   describe('vim.lsp.diagnostic.on_diagnostic', function()
@@ -489,7 +520,7 @@ describe('vim.lsp.diagnostic', function()
       eq(1, diagnostics[1].severity)
     end)
 
-    it('clears diagnostics when client detaches', function()
+    it('clears pull diagnostics when client detaches', function()
       exec_lua(function()
         vim.lsp.diagnostic.on_diagnostic(nil, {
           kind = 'full',