diff --git a/packages/metals-vscode/src/extension.ts b/packages/metals-vscode/src/extension.ts
index 3763132b..0c891e6d 100644
--- a/packages/metals-vscode/src/extension.ts
+++ b/packages/metals-vscode/src/extension.ts
@@ -192,6 +192,13 @@ async function fetchAndLaunchMetals(
   serverVersion: string,
   javaVersion: JavaVersion
 ) {
+  if (!workspace.workspaceFolders) {
+    const message = `Metals will not start because you've opened a single file and not a project directory.`;
+    window.showErrorMessage(message);
+    outputChannel.appendLine(message);
+    return;
+  }
+
   outputChannel.appendLine(`Metals version: ${serverVersion}`);
 
   /* eslint-disable @typescript-eslint/no-non-null-assertion */
@@ -214,9 +221,7 @@ async function fetchAndLaunchMetals(
   );
 
   const javaConfig = getJavaConfig({
-    workspaceRoot: workspace.workspaceFolders
-      ? workspace.workspaceFolders[0]?.uri.fsPath
-      : undefined,
+    workspaceRoot: workspace.workspaceFolders[0]?.uri.fsPath,
     javaHome,
     coursier,
     customRepositories,