diff --git a/packages/core/src/transform/diagnostics/augmentation.ts b/packages/core/src/transform/diagnostics/augmentation.ts
index 37c9103ef..55ba9bac5 100644
--- a/packages/core/src/transform/diagnostics/augmentation.ts
+++ b/packages/core/src/transform/diagnostics/augmentation.ts
@@ -2,7 +2,10 @@ import type ts from 'typescript';
 import { Diagnostic } from './index.js';
 import GlimmerASTMappingTree, { MappingSource } from '../template/glimmer-ast-mapping-tree.js';
 import TransformedModule from '../template/transformed-module.js';
+
 export function augmentDiagnostics<T extends Diagnostic>(
+  ts: typeof import('typescript'),
+  sourceFile: ts.SourceFile,
   transformedModule: TransformedModule,
   diagnostics: T[],
 ): T[] {
@@ -26,7 +29,11 @@ export function augmentDiagnostics<T extends Diagnostic>(
     return rangeWithMappingAndSource.mapping || null;
   };
 
-  const augmentedDiagnostics: T[] = [];
+  const unusedExpectErrors = new Set(
+    transformedModule.directives.filter((d) => d.kind === 'expect-error'),
+  );
+
+  const augmentedDiagnostics: Diagnostic[] = [];
 
   for (const diagnostic of diagnostics) {
     const augmentedDiagnostic = rewriteMessageText(diagnostic, mappingForDiagnostic);
@@ -41,15 +48,29 @@ export function augmentDiagnostics<T extends Diagnostic>(
       );
 
       if (appliedDirective) {
+        if (appliedDirective.kind === 'expect-error') {
+          unusedExpectErrors.delete(appliedDirective);
+        }
         // Filter out this diagnostic; its covered by a directive.
         continue;
       }
     }
 
-    // @ts-expect-error not sure how to fix
     augmentedDiagnostics.push(augmentedDiagnostic);
   }
 
+  for (const unusedExpectError of unusedExpectErrors) {
+    augmentedDiagnostics.push({
+      category: ts.DiagnosticCategory.Error,
+      code: 2578,
+      file: sourceFile,
+      start: unusedExpectError.location.start,
+      length: unusedExpectError.location.end - unusedExpectError.location.start,
+      messageText: `Unused '@glint-expect-error' directive.`,
+    });
+  }
+
+  // @ts-expect-error not sure how to fix
   return augmentedDiagnostics;
 }
 
diff --git a/packages/tsserver-plugin/src/typescript-server-plugin.ts b/packages/tsserver-plugin/src/typescript-server-plugin.ts
index e51c34d2a..520f1b967 100644
--- a/packages/tsserver-plugin/src/typescript-server-plugin.ts
+++ b/packages/tsserver-plugin/src/typescript-server-plugin.ts
@@ -202,7 +202,12 @@ function getSemanticDiagnostics<T>(
       return tsDiagnostics;
     }
 
-    const augmentedTsDiagnostics = augmentDiagnostics(transformedModule, tsDiagnostics);
+    const augmentedTsDiagnostics = augmentDiagnostics(
+      ts,
+      sourceFile,
+      transformedModule,
+      tsDiagnostics,
+    );
 
     return augmentedTsDiagnostics;
   };
diff --git a/test-packages/package-test-core/__tests__/language-server/diagnostics.test.ts b/test-packages/package-test-core/__tests__/language-server/diagnostics.test.ts
index f432d13f6..ce6ad8150 100644
--- a/test-packages/package-test-core/__tests__/language-server/diagnostics.test.ts
+++ b/test-packages/package-test-core/__tests__/language-server/diagnostics.test.ts
@@ -637,6 +637,43 @@ describe('Language Server: Diagnostics (ts plugin)', () => {
     `);
   });
 
+  test('unused @glint-expect-error triggers a diagnostic', async () => {
+    const componentA = stripIndent`
+      import Component from '@glimmer/component';
+
+      export default class ComponentA extends Component {
+        <template>
+          {{! @glint-expect-error }}
+          <Component />
+        </template>
+      }
+    `;
+
+    const diagnostics = await requestDiagnostics(
+      'ts-template-imports-app/src/ephemeral-index.gts',
+      'glimmer-ts',
+      componentA,
+    );
+
+    expect(diagnostics).toMatchInlineSnapshot(`
+      [
+        {
+          "category": "error",
+          "code": 2578,
+          "end": {
+            "line": 5,
+            "offset": 31,
+          },
+          "start": {
+            "line": 5,
+            "offset": 5,
+          },
+          "text": "Unused '@glint-expect-error' directive.",
+        },
+      ]
+    `);
+  });
+
   test('svg does not produce false positives', async () => {
     const code = stripIndent`
     import Component from '@glimmer/component';