diff --git a/runtime/lua/vim/diagnostic.lua b/runtime/lua/vim/diagnostic.lua
index 98dbe0779b..97065ac1ab 100644
--- a/runtime/lua/vim/diagnostic.lua
+++ b/runtime/lua/vim/diagnostic.lua
@@ -916,7 +916,7 @@ M.handlers.signs = {
   end,
   hide = function(namespace, bufnr)
     local ns = M.get_namespace(namespace)
-    if ns.user_data.sign_group then
+    if ns.user_data.sign_group and vim.api.nvim_buf_is_valid(bufnr) then
       vim.fn.sign_unplace(ns.user_data.sign_group, { buffer = bufnr })
     end
   end,
@@ -971,7 +971,9 @@ M.handlers.underline = {
     local ns = M.get_namespace(namespace)
     if ns.user_data.underline_ns then
       diagnostic_cache_extmarks[bufnr][ns.user_data.underline_ns] = {}
-      vim.api.nvim_buf_clear_namespace(bufnr, ns.user_data.underline_ns, 0, -1)
+      if vim.api.nvim_buf_is_valid(bufnr) then
+        vim.api.nvim_buf_clear_namespace(bufnr, ns.user_data.underline_ns, 0, -1)
+      end
     end
   end,
 }
@@ -1034,7 +1036,9 @@ M.handlers.virtual_text = {
     local ns = M.get_namespace(namespace)
     if ns.user_data.virt_text_ns then
       diagnostic_cache_extmarks[bufnr][ns.user_data.virt_text_ns] = {}
-      vim.api.nvim_buf_clear_namespace(bufnr, ns.user_data.virt_text_ns, 0, -1)
+      if vim.api.nvim_buf_is_valid(bufnr) then
+        vim.api.nvim_buf_clear_namespace(bufnr, ns.user_data.virt_text_ns, 0, -1)
+      end
     end
   end,
 }
@@ -1423,11 +1427,15 @@ function M.reset(namespace, bufnr)
       M.hide(iter_namespace, iter_bufnr)
     end
 
-    vim.api.nvim_exec_autocmds('DiagnosticChanged', {
-      modeline = false,
-      buffer = iter_bufnr,
-      data = { diagnostics = {} },
-    })
+    if vim.api.nvim_buf_is_valid(iter_bufnr) then
+      vim.api.nvim_exec_autocmds('DiagnosticChanged', {
+        modeline = false,
+        buffer = iter_bufnr,
+        data = { diagnostics = {} },
+      })
+    else
+      diagnostic_cache[iter_bufnr] = nil
+    end
   end
 end
 
diff --git a/test/functional/lua/diagnostic_spec.lua b/test/functional/lua/diagnostic_spec.lua
index 28a8679205..506c2097c9 100644
--- a/test/functional/lua/diagnostic_spec.lua
+++ b/test/functional/lua/diagnostic_spec.lua
@@ -159,6 +159,24 @@ describe('vim.diagnostic', function()
     ]])
   end)
 
+  it('removes diagnostic from stale cache on reset', function()
+    local diagnostics = exec_lua [[
+      vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, {
+        make_error('Diagnostic #1', 1, 1, 1, 1),
+        make_error('Diagnostic #2', 2, 1, 2, 1),
+      })
+      local other_bufnr = vim.fn.bufadd('test | test')
+      vim.cmd('noautocmd bwipeout! ' .. diagnostic_bufnr)
+      return vim.diagnostic.get(diagnostic_bufnr)
+    ]]
+    eq(2, #diagnostics)
+    diagnostics = exec_lua [[
+      vim.diagnostic.reset()
+      return vim.diagnostic.get()
+    ]]
+    eq(0, #diagnostics)
+  end)
+
   it('resolves buffer number 0 to the current buffer', function()
     eq(2, exec_lua [[
       vim.api.nvim_set_current_buf(diagnostic_bufnr)