diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 8c0d802..ab1f6f7 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -22,7 +22,7 @@
 # be identified in the format @org/team-name. Teams must have
 # explicit write access to the repository. In this example,
 # the octocats team in the octo-org organization owns all .txt files.
-*.txt @octo-org/octocats
+*.txt @octo-org/@test_one/octocats
 
 # In this example, @doctocat owns any files in the build/logs
 # directory at the root of the repository and any of its
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26da346..d1e568c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## 4.2.0 - 2026-03-14
+
+### Added
+
+- Show error diagnostics for invalid CODEOWNERS patterns (#34).
+
 ## 4.1.0 - 2024-04-13
 
 ### Changed
diff --git a/package-lock.json b/package-lock.json
index b822d89..0bcc889 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,15 +1,15 @@
 {
   "name": "github-code-owners",
-  "version": "4.1.0",
+  "version": "4.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "github-code-owners",
-      "version": "4.1.0",
+      "version": "4.2.0",
       "license": "SEE LICENSE IN LICENSE",
       "dependencies": {
-        "@snyk/github-codeowners": "github:chdsbd/github-codeowners#chris/line-number-information",
+        "@snyk/github-codeowners": "github:chdsbd/github-codeowners#da8b03fa3cb4de086f3a564f1af03cc44288e43c",
         "lodash": "^4.17.21"
       },
       "devDependencies": {
@@ -632,7 +632,8 @@
       }
     },
     "node_modules/@snyk/github-codeowners": {
-      "resolved": "git+ssh://git@github.com/chdsbd/github-codeowners.git#64dc4df353de62f0c96dae96897e283e66d5be37",
+      "resolved": "git+ssh://git@github.com/chdsbd/github-codeowners.git#da8b03fa3cb4de086f3a564f1af03cc44288e43c",
+      "integrity": "sha512-sKJAAPWO++0CBHEuWxljAdJdgj/7OtAQHUzxWlFjZmKvDuAPtyEOz8Mi9nXqveZx1z1egcxMXoClM90br0jAeg==",
       "license": "MIT",
       "dependencies": {
         "commander": "^4.1.1",
@@ -643,7 +644,7 @@
         "github-codeowners": "dist/cli.js"
       },
       "engines": {
-        "node": ">=8.10"
+        "node": ">=22"
       }
     },
     "node_modules/@snyk/github-codeowners/node_modules/commander": {
diff --git a/package.json b/package.json
index ece2ea5..baf2ccc 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "Quickly see GitHub Code Owners for the current file. Add syntax highlighting for CODEOWNERS files.",
   "publisher": "chdsbd",
   "license": "SEE LICENSE IN LICENSE",
-  "version": "4.1.0",
+  "version": "4.2.0",
   "icon": "images/logo256.png",
   "homepage": "https://github.com/chdsbd/vscode-github-code-owners/blob/master/README.md",
   "keywords": [
@@ -229,7 +229,7 @@
     "typescript": "^4.9.5"
   },
   "dependencies": {
-    "@snyk/github-codeowners": "github:chdsbd/github-codeowners#chris/line-number-information",
+    "@snyk/github-codeowners": "github:chdsbd/github-codeowners#da8b03fa3cb4de086f3a564f1af03cc44288e43c",
     "lodash": "^4.17.21"
   },
   "volta": {
diff --git a/src/codeowners-diagnostic-provider.ts b/src/codeowners-diagnostic-provider.ts
new file mode 100644
index 0000000..7e48ee4
--- /dev/null
+++ b/src/codeowners-diagnostic-provider.ts
@@ -0,0 +1,49 @@
+import vscode from "vscode"
+import { OwnershipEngine } from "@snyk/github-codeowners/dist/lib/ownership"
+
+function updateDiagnostics(
+  document: vscode.TextDocument,
+  collection: vscode.DiagnosticCollection,
+): void {
+  if (document.languageId !== "codeowners") {
+    return
+  }
+
+  const engine = OwnershipEngine.FromCodeownersFile(document.uri.fsPath)
+
+  const diagnostics = engine.errors.map((err) => {
+    const line = document.lineAt(err.lineno)
+    return new vscode.Diagnostic(line.range, err.message, vscode.DiagnosticSeverity.Error)
+  })
+
+  collection.set(document.uri, diagnostics)
+}
+
+export function registerCodeownersDiagnostics(
+  context: vscode.ExtensionContext,
+): void {
+  const collection = vscode.languages.createDiagnosticCollection("codeowners")
+  context.subscriptions.push(collection)
+
+  vscode.workspace.textDocuments.forEach((doc) =>
+    updateDiagnostics(doc, collection),
+  )
+
+  vscode.workspace.onDidOpenTextDocument(
+    (doc) => updateDiagnostics(doc, collection),
+    null,
+    context.subscriptions,
+  )
+
+  vscode.workspace.onDidChangeTextDocument(
+    (e) => updateDiagnostics(e.document, collection),
+    null,
+    context.subscriptions,
+  )
+
+  vscode.workspace.onDidCloseTextDocument(
+    (doc) => collection.delete(doc.uri),
+    null,
+    context.subscriptions,
+  )
+}
diff --git a/src/extension.ts b/src/extension.ts
index e6068b4..648ff96 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -7,6 +7,7 @@ import { showOwnersCommandHandler } from "./show-owners-command"
 import { CodeownersHoverProvider } from "./codeowners-hover-provider"
 import { statusBarTextEditorListener } from "./status-bar-text-editor-listener"
 import { AlignOwnersFormattingProvider } from "./align-codeowners"
+import { registerCodeownersDiagnostics } from "./codeowners-diagnostic-provider"
 
 const COMMAND_ID = "github-code-owners.show-owners"
 
@@ -74,6 +75,8 @@ export function activate(context: vscode.ExtensionContext) {
     ),
   )
 
+  registerCodeownersDiagnostics(context)
+
   vscode.workspace.onDidChangeConfiguration(() => {
     outputChannel.appendLine("Configuration changed: Reloading link provider")
     handles.linkProvider.dispose()