diff --git a/extensions/markdown-language-features/src/preview/preview.ts b/extensions/markdown-language-features/src/preview/preview.ts
index 1a7a859d446..19d1755e7eb 100644
--- a/extensions/markdown-language-features/src/preview/preview.ts
+++ b/extensions/markdown-language-features/src/preview/preview.ts
@@ -110,15 +110,17 @@ class MarkdownPreview extends Disposable implements WebviewResourceProvider {
 			}
 		}));
 
-		const watcher = this._register(vscode.workspace.createFileSystemWatcher(new vscode.RelativePattern(resource, '*')));
-		this._register(watcher.onDidChange(uri => {
-			if (this.isPreviewOf(uri)) {
-				// Only use the file system event when VS Code does not already know about the file
-				if (!vscode.workspace.textDocuments.some(doc => doc.uri.toString() === uri.toString())) {
-					this.refresh();
+		if (vscode.workspace.fs.isWritableFileSystem(resource.scheme)) {
+			const watcher = this._register(vscode.workspace.createFileSystemWatcher(new vscode.RelativePattern(resource, '*')));
+			this._register(watcher.onDidChange(uri => {
+				if (this.isPreviewOf(uri)) {
+					// Only use the file system event when VS Code does not already know about the file
+					if (!vscode.workspace.textDocuments.some(doc => doc.uri.toString() === uri.toString())) {
+						this.refresh();
+					}
 				}
-			}
-		}));
+			}));
+		}
 
 		this._register(this._webviewPanel.webview.onDidReceiveMessage((e: FromWebviewMessage.Type) => {
 			if (e.source !== this._resource.toString()) {