diff --git a/protocol/src/common/protocol.diagnostic.ts b/protocol/src/common/protocol.diagnostic.ts
index 8971b12c6..abb82d23d 100644
--- a/protocol/src/common/protocol.diagnostic.ts
+++ b/protocol/src/common/protocol.diagnostic.ts
@@ -109,7 +109,7 @@ export type DiagnosticServerCancellationData = {
 export namespace DiagnosticServerCancellationData {
 	export function is(value: any): value is DiagnosticServerCancellationData {
 		const candidate = value as DiagnosticServerCancellationData;
-		return candidate && Is.boolean(candidate.retriggerRequest);
+		return Is.objectLiteral(candidate) && Is.boolean(candidate.retriggerRequest);
 	}
 }
 
diff --git a/protocol/src/common/protocol.ts b/protocol/src/common/protocol.ts
index 97e60d9fa..b5d0025f3 100644
--- a/protocol/src/common/protocol.ts
+++ b/protocol/src/common/protocol.ts
@@ -1188,7 +1188,7 @@ export namespace WorkDoneProgressOptions {
 	}
 	export function hasWorkDoneProgress(value: any): value is { workDoneProgress: boolean } {
 		const candidate = value as WorkDoneProgressOptions;
-		return candidate && Is.boolean(candidate.workDoneProgress);
+		return Is.objectLiteral(candidate) && Is.boolean(candidate.workDoneProgress);
 	}
 }
 
diff --git a/protocol/src/node/test/documentFilter.test.ts b/protocol/src/node/test/documentFilter.test.ts
index 51237e834..cd0375270 100644
--- a/protocol/src/node/test/documentFilter.test.ts
+++ b/protocol/src/node/test/documentFilter.test.ts
@@ -6,25 +6,15 @@
 
 import * as assert from 'assert';
 
-import { DocumentSelector, NotebookCellTextDocumentFilter, NotebookDocumentFilter, RelativePattern, TextDocumentFilter, TextDocumentRegistrationOptions } from '../main';
+import {
+	DiagnosticServerCancellationData, DocumentSelector, NotebookCellTextDocumentFilter, NotebookDocumentFilter,
+	RelativePattern, TextDocumentFilter, TextDocumentRegistrationOptions, WorkDoneProgressOptions
+} from '../main';
 
 suite('Document filter type guards', () => {
 
 	const relativePattern: RelativePattern = { baseUri: 'file:///workspace', pattern: '**/*.ipynb' };
 
-	suite('TextDocumentFilter.is', () => {
-		test('valid filters', () => {
-			assert.strictEqual(TextDocumentFilter.is('typescript'), true);
-			assert.strictEqual(TextDocumentFilter.is({ language: 'typescript' }), true);
-			assert.strictEqual(TextDocumentFilter.is({ scheme: 'file' }), true);
-			assert.strictEqual(TextDocumentFilter.is({ pattern: '**/*.ts' }), true);
-		});
-		test('null and undefined', () => {
-			assert.strictEqual(TextDocumentFilter.is(null), false);
-			assert.strictEqual(TextDocumentFilter.is(undefined), false);
-		});
-	});
-
 	suite('NotebookDocumentFilter.is', () => {
 		test('string pattern', () => {
 			assert.strictEqual(NotebookDocumentFilter.is({ pattern: '**/*.ipynb' }), true);
@@ -54,20 +44,81 @@ suite('Document filter type guards', () => {
 		});
 	});
 
-	suite('DocumentSelector.is', () => {
-		test('null and undefined elements', () => {
-			assert.strictEqual(DocumentSelector.is([null as any]), false);
-			assert.strictEqual(DocumentSelector.is([undefined as any]), false);
+	suite('TextDocumentFilter.is', () => {
+		test('string filter', () => {
+			assert.strictEqual(TextDocumentFilter.is('typescript'), true);
+		});
+		test('language filter', () => {
+			assert.strictEqual(TextDocumentFilter.is({ language: 'typescript' }), true);
+		});
+		test('scheme filter', () => {
+			assert.strictEqual(TextDocumentFilter.is({ scheme: 'file' }), true);
+		});
+		test('pattern filter with string pattern', () => {
+			assert.strictEqual(TextDocumentFilter.is({ pattern: '**/*.ts' }), true);
+		});
+		test('pattern filter with relative pattern', () => {
+			assert.strictEqual(TextDocumentFilter.is({ pattern: relativePattern }), true);
 		});
+		test('null and undefined', () => {
+			assert.strictEqual(TextDocumentFilter.is(null), false);
+			assert.strictEqual(TextDocumentFilter.is(undefined), false);
+		});
+		test('invalid values', () => {
+			assert.strictEqual(TextDocumentFilter.is({}), false);
+			assert.strictEqual(TextDocumentFilter.is(123), false);
+			assert.strictEqual(TextDocumentFilter.is(true), false);
+			assert.strictEqual(TextDocumentFilter.is({ pattern: 123 }), false);
+		});
+	});
+
+	suite('DocumentSelector.is', () => {
 		test('notebook cell filter with relative pattern', () => {
 			const documentSelector = [{ notebook: { pattern: relativePattern } }];
 			assert.strictEqual(DocumentSelector.is(documentSelector), true);
 			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector }), true);
 		});
-		test('TextDocumentRegistrationOptions.is with null and undefined', () => {
+		test('null and undefined elements', () => {
+			assert.strictEqual(DocumentSelector.is([null as any]), false);
+			assert.strictEqual(DocumentSelector.is([undefined as any]), false);
+			assert.strictEqual(DocumentSelector.is(['typescript', null as any]), false);
+		});
+		test('null and undefined selector', () => {
+			assert.strictEqual(DocumentSelector.is(null), false);
+			assert.strictEqual(DocumentSelector.is(undefined), false);
+		});
+	});
+
+	suite('TextDocumentRegistrationOptions.is', () => {
+		test('valid registration options', () => {
+			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector: ['typescript'] }), true);
+			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector: null }), true);
+		});
+		test('invalid registration options', () => {
+			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector: [null] }), false);
+			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector: [undefined] }), false);
+		});
+		test('null and undefined', () => {
 			assert.strictEqual(TextDocumentRegistrationOptions.is(null), false);
 			assert.strictEqual(TextDocumentRegistrationOptions.is(undefined), false);
-			assert.strictEqual(TextDocumentRegistrationOptions.is({ documentSelector: [null] }), false);
+			assert.strictEqual(TextDocumentRegistrationOptions.is(123), false);
+		});
+	});
+
+	suite('WorkDoneProgressOptions and DiagnosticServerCancellationData null handling', () => {
+		test('WorkDoneProgressOptions.hasWorkDoneProgress', () => {
+			assert.strictEqual(WorkDoneProgressOptions.hasWorkDoneProgress({ workDoneProgress: true }), true);
+			assert.strictEqual(WorkDoneProgressOptions.hasWorkDoneProgress({ workDoneProgress: false }), true);
+			assert.strictEqual(WorkDoneProgressOptions.hasWorkDoneProgress({}), false);
+			assert.strictEqual(WorkDoneProgressOptions.hasWorkDoneProgress(null), false);
+			assert.strictEqual(WorkDoneProgressOptions.hasWorkDoneProgress(undefined), false);
+		});
+		test('DiagnosticServerCancellationData.is', () => {
+			assert.strictEqual(DiagnosticServerCancellationData.is({ retriggerRequest: true }), true);
+			assert.strictEqual(DiagnosticServerCancellationData.is({ retriggerRequest: false }), true);
+			assert.strictEqual(DiagnosticServerCancellationData.is({}), false);
+			assert.strictEqual(DiagnosticServerCancellationData.is(null), false);
+			assert.strictEqual(DiagnosticServerCancellationData.is(undefined), false);
 		});
 	});
 });