diff --git a/yarn-project/acir-simulator/src/abi_coder/decoder.ts b/yarn-project/acir-simulator/src/abi_coder/decoder.ts
index 9571f63a5aee..d83b0ed35eda 100644
--- a/yarn-project/acir-simulator/src/abi_coder/decoder.ts
+++ b/yarn-project/acir-simulator/src/abi_coder/decoder.ts
@@ -1,6 +1,11 @@
 import { Fr } from '@aztec/foundation/fields';
 import { ABIType, FunctionAbi } from '@aztec/foundation/abi';
 
+/**
+ * The type of our decoded ABI.
+ */
+type DecodedReturn = bigint | boolean | DecodedReturn[] | { [key: string]: DecodedReturn };
+
 /**
  * Decodes return values from a function call.
  * Missing support for integer and string.
@@ -13,7 +18,7 @@ class ReturnValuesDecoder {
    * @param abiType - The type of the return value.
    * @returns The decoded return value.
    */
-  private decodeReturn(abiType: ABIType): any {
+  private decodeReturn(abiType: ABIType): DecodedReturn {
     switch (abiType.kind) {
       case 'field':
         return this.getNextField().value;
@@ -24,14 +29,14 @@ class ReturnValuesDecoder {
         for (let i = 0; i < abiType.length; i += 1) {
           array.push(this.decodeReturn(abiType.type));
         }
-        break;
+        return array;
       }
       case 'struct': {
-        const struct: any = {};
+        const struct: { [key: string]: DecodedReturn } = {};
         for (const field of abiType.fields) {
           struct[field.name] = this.decodeReturn(field.type);
         }
-        break;
+        return struct;
       }
       default:
         throw new Error(`Unsupported type: ${abiType.kind}`);