diff --git a/src/guards.ts b/src/guards.ts
index 8e9f3030..ae8eeeb3 100644
--- a/src/guards.ts
+++ b/src/guards.ts
@@ -41,7 +41,7 @@ export function isThing(something: unknown): something is SCThing {
 
   return Object
     .values(SCThingType)
-    .indexOf(type) >= 0;
+    .indexOf(type as SCThingType) >= 0;
 }
 
 /**