diff --git a/extensions/copilot/src/platform/languages/vscode/languageDiagnosticsServiceImpl.ts b/extensions/copilot/src/platform/languages/vscode/languageDiagnosticsServiceImpl.ts
index 5af945d1b66..6505f80f3ab 100644
--- a/extensions/copilot/src/platform/languages/vscode/languageDiagnosticsServiceImpl.ts
+++ b/extensions/copilot/src/platform/languages/vscode/languageDiagnosticsServiceImpl.ts
@@ -4,18 +4,46 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as vscode from 'vscode';
+import { ILogService } from '../../log/common/logService';
 import { AbstractLanguageDiagnosticsService } from '../common/languageDiagnosticsService';
 
 export class LanguageDiagnosticsServiceImpl extends AbstractLanguageDiagnosticsService {
 	private static ignoredSchemes = new Set(['git', 'chat-editing-snapshot-text-model', 'chat-editing-text-model']);
 	override onDidChangeDiagnostics: vscode.Event<vscode.DiagnosticChangeEvent> = vscode.languages.onDidChangeDiagnostics;
 
+	constructor(
+		@ILogService private readonly _logService: ILogService,
+	) {
+		super();
+	}
+
 	override getDiagnostics(resource: vscode.Uri): vscode.Diagnostic[] {
-		return vscode.languages.getDiagnostics(resource);
+		return this._dropMalformedDiagnostics(vscode.languages.getDiagnostics(resource));
 	}
 
 	override getAllDiagnostics(): [vscode.Uri, vscode.Diagnostic[]][] {
 		return vscode.languages.getDiagnostics()
-			.filter(([uri]) => !LanguageDiagnosticsServiceImpl.ignoredSchemes.has(uri.scheme));
+			.filter(([uri]) => !LanguageDiagnosticsServiceImpl.ignoredSchemes.has(uri.scheme))
+			.map(([uri, diagnostics]): [vscode.Uri, vscode.Diagnostic[]] => [uri, this._dropMalformedDiagnostics(diagnostics)]);
+	}
+
+	/**
+	 * Diagnostics are produced by arbitrary extensions and reach us verbatim through the
+	 * `vscode.languages.getDiagnostics` API. An extension can publish an entry that violates the
+	 * {@link vscode.Diagnostic} contract at runtime - most notably with a missing `range` assigned
+	 * through an `any` cast - and such an entry crashes the many consumers that dereference
+	 * `diagnostic.range`. Drop the malformed entries here, at the extension boundary, and surface
+	 * the occurrence so the underlying producer stays diagnosable.
+	 */
+	private _dropMalformedDiagnostics(diagnostics: vscode.Diagnostic[]): vscode.Diagnostic[] {
+		const valid = diagnostics.filter(diagnostic => {
+			const range: vscode.Range | null | undefined = diagnostic.range;
+			return range !== null && range !== undefined;
+		});
+		const dropped = diagnostics.length - valid.length;
+		if (dropped > 0) {
+			this._logService.warn(`[LanguageDiagnosticsService] Ignored ${dropped} diagnostic(s) with a missing range received from the diagnostics API.`);
+		}
+		return valid;
 	}
 }