diff --git a/src/vs/workbench/api/browser/mainThreadDiagnostics.ts b/src/vs/workbench/api/browser/mainThreadDiagnostics.ts
index 94fafb8b6b1..8a7cff3c95e 100644
--- a/src/vs/workbench/api/browser/mainThreadDiagnostics.ts
+++ b/src/vs/workbench/api/browser/mainThreadDiagnostics.ts
@@ -37,12 +37,14 @@ export class MainThreadDiagnostics implements MainThreadDiagnosticsShape {
 	private _forwardMarkers(resources: readonly URI[]): void {
 		const data: [UriComponents, IMarkerData[]][] = [];
 		for (const resource of resources) {
-			data.push([
-				resource,
-				this._markerService.read({ resource }).filter(marker => !this._activeOwners.has(marker.owner))
-			]);
+			const markerData = this._markerService.read({ resource }).filter(marker => !this._activeOwners.has(marker.owner));
+			if (markerData.length > 0) {
+				data.push([resource, markerData]);
+			}
+		}
+		if (data.length > 0) {
+			this._proxy.$acceptMarkersChange(data);
 		}
-		this._proxy.$acceptMarkersChange(data);
 	}
 
 	$changeMany(owner: string, entries: [UriComponents, IMarkerData[]][]): void {
diff --git a/src/vs/workbench/test/browser/api/mainThreadDiagnostics.test.ts b/src/vs/workbench/test/browser/api/mainThreadDiagnostics.test.ts
index 5a16d7d6b92..7b3c74f0457 100644
--- a/src/vs/workbench/test/browser/api/mainThreadDiagnostics.test.ts
+++ b/src/vs/workbench/test/browser/api/mainThreadDiagnostics.test.ts
@@ -6,11 +6,14 @@
 import * as assert from 'assert';
 import { MarkerService } from 'vs/platform/markers/common/markerService';
 import { MainThreadDiagnostics } from 'vs/workbench/api/browser/mainThreadDiagnostics';
-import { URI } from 'vs/base/common/uri';
+import { URI, UriComponents } from 'vs/base/common/uri';
 import { IExtHostContext } from 'vs/workbench/api/common/extHost.protocol';
 import { mock } from 'vs/workbench/test/common/workbenchTestServices';
 import { IUriIdentityService } from 'vs/platform/uriIdentity/common/uriIdentity';
 import { ExtensionHostKind } from 'vs/workbench/services/extensions/common/extensions';
+import { IMarkerData } from 'vs/platform/markers/common/markers';
+import { runWithFakedTimers } from 'vs/base/test/common/timeTravelScheduler';
+import { timeout } from 'vs/base/common/async';
 
 
 suite('MainThreadDiagnostics', function () {
@@ -57,4 +60,54 @@ suite('MainThreadDiagnostics', function () {
 		diag.dispose();
 		assert.strictEqual(markerService.read().length, 0);
 	});
+
+	test('OnDidChangeDiagnostics triggers twice on same diagnostics #136434', function () {
+
+		return runWithFakedTimers({}, async () => {
+
+			const changedData: [UriComponents, IMarkerData[]][][] = [];
+
+			let diag = new MainThreadDiagnostics(
+				new class implements IExtHostContext {
+					remoteAuthority = '';
+					extensionHostKind = ExtensionHostKind.LocalProcess;
+					assertRegistered() { }
+					set(v: any): any { return null; }
+					getProxy(): any {
+						return {
+							$acceptMarkersChange(data: [UriComponents, IMarkerData[]][]) {
+								changedData.push(data);
+							}
+						};
+					}
+					drain(): any { return null; }
+				},
+				markerService,
+				new class extends mock<IUriIdentityService>() {
+					override asCanonicalUri(uri: URI) { return uri; }
+				}
+			);
+
+			const markerDataStub = {
+				code: '666',
+				startLineNumber: 1,
+				startColumn: 1,
+				endLineNumber: 1,
+				endColumn: 1,
+				severity: 1,
+				source: 'me'
+			};
+			const target = URI.file('a');
+			diag.$changeMany('foo', [[target, [{ ...markerDataStub, message: 'same_owner' }]]]);
+			markerService.changeOne('bar', target, [{ ...markerDataStub, message: 'forgein_owner' }]);
+
+			// added one marker via the API and one via the ext host. the latter must not
+			// trigger an event to the extension host
+
+			await timeout(0);
+			assert.strictEqual(markerService.read().length, 2);
+			assert.strictEqual(changedData.length, 1);
+			assert.strictEqual(changedData[0][0][1][0].message, 'forgein_owner');
+		});
+	});
 });