diff --git a/ts/src/program/namespace/types.ts b/ts/src/program/namespace/types.ts
index 5c80411abc..be278dfde6 100644
--- a/ts/src/program/namespace/types.ts
+++ b/ts/src/program/namespace/types.ts
@@ -107,7 +107,7 @@ export type DecodeType<T extends IdlType, Defined> = T extends keyof TypeMap
   : T extends { option: { defined: keyof Defined } }
   ? Defined[T["option"]["defined"]] | null
   : T extends { option: keyof TypeMap }
-  ? TypeMap[T["option"]]
+  ? TypeMap[T["option"]] | null
   : T extends { vec: keyof TypeMap }
   ? TypeMap[T["vec"]][]
   : T extends { array: [defined: keyof TypeMap, size: number] }