diff --git a/phet-types.d.ts b/phet-types.d.ts
index 860ebf7d..965cc1b1 100644
--- a/phet-types.d.ts
+++ b/phet-types.d.ts
@@ -20,6 +20,8 @@ declare var phet: any;
 type PaintDef = Paint | Color | string | Property<null | string | Color>;
 type ColorDef = Color | string | null | Property<null | string | Color>;
 
+type AlertableDef = string | number | ResponsePacket | Utterance;
+
 type ScreenViewOptions = Partial<{
   layoutBounds: Bounds2,
   layerSplit: boolean,