diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index e48ce71fb1a..3de4a7af9dd 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -357,8 +357,8 @@ declare module 'vscode' {
 
 	//todo@joh -> make class
 	export interface DecorationData {
-		letter: string;
-		title: string;
+		letter?: string;
+		title?: string;
 		color?: ThemeColor;
 		priority?: number;
 		bubble?: boolean;
diff --git a/src/vs/workbench/api/node/extHostDecorations.ts b/src/vs/workbench/api/node/extHostDecorations.ts
index 4ffee738596..1cc31088fe1 100644
--- a/src/vs/workbench/api/node/extHostDecorations.ts
+++ b/src/vs/workbench/api/node/extHostDecorations.ts
@@ -53,8 +53,8 @@ export class ExtHostDecorations implements ExtHostDecorationsShape {
 			}
 			const { provider, extensionId } = this._provider.get(handle);
 			return asWinJsPromise(token => provider.provideDecoration(URI.revive(uri), token)).then(data => {
-				if (!data.letter || data.letter.length !== 1) {
-					console.warn(`INVALID decoration from extension '${extensionId}'. The 'letter' must be set and be one character`);
+				if (data.letter && data.letter.length !== 1) {
+					console.warn(`INVALID decoration from extension '${extensionId}'. The 'letter' must be set and be one character, not '${data.letter}'.`);
 				}
 				result[id] = data && <DecorationData>[data.priority, data.bubble, data.title, data.letter, data.color, data.source];
 			}, err => {