diff --git a/src/transactions/decoders.ts b/src/transactions/decoders.ts
index 33e799f..f5f3350 100644
--- a/src/transactions/decoders.ts
+++ b/src/transactions/decoders.ts
@@ -142,6 +142,21 @@ export const simplifyTransactionReceipt = (tx: GenLayerTransaction): GenLayerTra
       return obj.map(item => simplifyObject(item, path)).filter(item => item !== undefined);
     }
 
+    // Decoded calldata (`txDataDecoded.callData` / `constructorArgs`, see
+    // abi/calldata/decoder.ts's TYPE_MAP) is a `Map<string, CalldataEncodable>`,
+    // not a plain object. `Object.entries()` below only sees a plain object's
+    // own enumerable properties, so a Map falls through it as `{}` — the
+    // decoded method name and arguments are silently dropped instead of
+    // simplified. Convert it to a plain object first so its entries go
+    // through the same simplification as everything else.
+    if (obj instanceof Map) {
+      const result: any = {};
+      for (const [key, value] of obj.entries()) {
+        result[key] = simplifyObject(value, path ? `${path}.${key}` : key);
+      }
+      return result;
+    }
+
     if (typeof obj === "object") {
       const result: any = {};
       
diff --git a/tests/transactions.test.ts b/tests/transactions.test.ts
index 548c57e..b803c54 100644
--- a/tests/transactions.test.ts
+++ b/tests/transactions.test.ts
@@ -1112,4 +1112,40 @@ describe("simplifyTransactionReceipt", () => {
     expect(genvm.stderr).toBe("some error");
     expect(genvm.exit_code).toBe(1);
   });
+
+  it("should preserve decoded calldata Map (method + args) instead of dropping it", () => {
+    // Matches decodeCalldata's TYPE_MAP output: a Map<string, CalldataEncodable>,
+    // not a plain object.
+    const tx = {
+      txDataDecoded: {
+        callData: new Map<string, unknown>([
+          ["", "inspect_delivery"],
+          ["args", ["synthetic-reference"]],
+        ]),
+        leaderOnly: false,
+        type: "call",
+      },
+    } as any;
+
+    const simplified = simplifyTransactionReceipt(tx) as any;
+
+    expect(simplified.txDataDecoded.callData).toEqual({
+      "": "inspect_delivery",
+      args: ["synthetic-reference"],
+    });
+    expect(simplified.txDataDecoded.leaderOnly).toBe(false);
+  });
+
+  it("should preserve a Map-shaped constructorArgs the same way", () => {
+    const tx = {
+      txDataDecoded: {
+        constructorArgs: new Map<string, unknown>([["owner", "0xabc"]]),
+        type: "deploy",
+      },
+    } as any;
+
+    const simplified = simplifyTransactionReceipt(tx) as any;
+
+    expect(simplified.txDataDecoded.constructorArgs).toEqual({owner: "0xabc"});
+  });
 });