diff --git a/src/stores/widgets/StopGapWidgetDriver.ts b/src/stores/widgets/StopGapWidgetDriver.ts
index 84626e74fb..b54e4a5f7d 100644
--- a/src/stores/widgets/StopGapWidgetDriver.ts
+++ b/src/stores/widgets/StopGapWidgetDriver.ts
@@ -25,6 +25,6 @@ export class StopGapWidgetDriver extends WidgetDriver {
     }
 
     public async validateCapabilities(requested: Set<Capability>): Promise<Set<Capability>> {
-        return iterableUnion(requested, new Set(this.allowedCapabilities));
+        return new Set(iterableUnion(requested, this.allowedCapabilities));
     }
 }
diff --git a/src/utils/iterables.ts b/src/utils/iterables.ts
index 3d2585906d..56e0bca1b7 100644
--- a/src/utils/iterables.ts
+++ b/src/utils/iterables.ts
@@ -16,6 +16,6 @@
 
 import { arrayUnion } from "./arrays";
 
-export function iterableUnion<C extends Iterable<T>, T>(a: C, b: C): Set<T> {
-    return new Set(arrayUnion(Array.from(a), Array.from(b)));
+export function iterableUnion<T>(a: Iterable<T>, b: Iterable<T>): Iterable<T> {
+    return arrayUnion(Array.from(a), Array.from(b));
 }