diff --git a/extensions/markdown-language-features/src/features/preview.ts b/extensions/markdown-language-features/src/features/preview.ts
index 8a357a2ff68..37a21b493fa 100644
--- a/extensions/markdown-language-features/src/features/preview.ts
+++ b/extensions/markdown-language-features/src/features/preview.ts
@@ -28,6 +28,8 @@ export class MarkdownPreview {
 	private currentVersion?: { resource: vscode.Uri, version: number };
 	private forceUpdate = false;
 	private isScrolling = false;
+	private _disposed: boolean = false;
+
 
 	public static async revive(
 		webview: vscode.Webview,
@@ -141,7 +143,7 @@ export class MarkdownPreview {
 
 		vscode.window.onDidChangeTextEditorSelection(event => {
 			if (this.isPreviewOf(event.textEditor.document.uri)) {
-				this.webview.postMessage({
+				this.postMessage({
 					type: 'onDidChangeTextEditorSelection',
 					line: event.selections[0].active.line,
 					source: this.resource.toString()
@@ -169,6 +171,11 @@ export class MarkdownPreview {
 	}
 
 	public dispose() {
+		if (this._disposed) {
+			return;
+		}
+
+		this._disposed = true;
 		this._onDisposeEmitter.fire();
 
 		this._onDisposeEmitter.dispose();
@@ -276,7 +283,7 @@ export class MarkdownPreview {
 		if (typeof topLine === 'number') {
 			this.logger.log('updateForView', { markdownFile: resource });
 			this.line = topLine;
-			this.webview.postMessage({
+			this.postMessage({
 				type: 'updateView',
 				line: topLine,
 				source: resource.toString()
@@ -284,6 +291,12 @@ export class MarkdownPreview {
 		}
 	}
 
+	private postMessage(msg: any) {
+		if (!this._disposed) {
+			this.webview.postMessage(msg);
+		}
+	}
+
 	private async doUpdate(): Promise<void> {
 		const resource = this._resource;