diff --git a/src/transaction.js b/src/transaction.js
index 1e585a61d..58b3bb5b0 100644
--- a/src/transaction.js
+++ b/src/transaction.js
@@ -74,6 +74,7 @@ class Transaction {
         }
         if (appArgs !== undefined) {
             if (!Array.isArray(appArgs)) throw Error("appArgs must be an Array of Uint8Array.");
+            appArgs = appArgs.slice();
             appArgs.forEach((arg) => {
                 if (arg.constructor !== Uint8Array) throw Error("each element of AppArgs must be a Uint8Array.");
             });
@@ -81,16 +82,19 @@ class Transaction {
             appArgs = new Uint8Array(0);
         }
         if (appAccounts !== undefined) {
-            appAccounts.forEach((addressAsString, index) => {
-               appAccounts[index] = address.decodeAddress(addressAsString);
-            })
+            if (!Array.isArray(appAccounts)) throw Error("appAccounts must be an Array of addresses.");
+            appAccounts = appAccounts.map(addressAsString => address.decodeAddress(addressAsString));
         }
         if (appForeignApps !== undefined) {
+            if (!Array.isArray(appForeignApps)) throw Error("appForeignApps must be an Array of integers.");
+            appForeignApps = appForeignApps.slice();
             appForeignApps.forEach((foreignAppIndex) => {
                if (!Number.isSafeInteger(foreignAppIndex) || foreignAppIndex < 0) throw Error("each foreign application index must be a positive number and smaller than 2^53-1");
             });
         }
         if (appForeignAssets !== undefined) {
+            if (!Array.isArray(appForeignAssets)) throw Error("appForeignAssets must be an Array of integers.");
+            appForeignAssets = appForeignAssets.slice();
             appForeignAssets.forEach((foreignAssetIndex) => {
                 if (!Number.isSafeInteger(foreignAssetIndex) || foreignAssetIndex < 0) throw Error("each foreign asset index must be a positive number and smaller than 2^53-1");
             });
@@ -396,16 +400,10 @@ class Transaction {
                 txn.apsu = Buffer.from(this.appClearProgram);
             }
             if (this.appArgs !== undefined) {
-                txn.apaa = [];
-                this.appArgs.forEach((arg) => {
-                    txn.apaa.push(Buffer.from(arg));
-                });
+                txn.apaa = this.appArgs.map(arg => Buffer.from(arg));
             }
             if (this.appAccounts !== undefined) {
-                txn.apat = [];
-                this.appAccounts.forEach((decodedAddress) => {
-                    txn.apat.push(Buffer.from(decodedAddress.publicKey));
-                });
+                txn.apat = this.appAccounts.map(decodedAddress => Buffer.from(decodedAddress.publicKey));
             }
             // allowed zero values
             if (!txn.note.length) delete txn.note;
@@ -524,16 +522,10 @@ class Transaction {
                 txn.appClearProgram = new Uint8Array(txnForEnc.apsu);
             }
             if (txnForEnc.apaa !== undefined) {
-                txn.appArgs = [];
-                txnForEnc.apaa.forEach((arg) => {
-                    txn.appArgs.push(new Uint8Array(arg));
-                });
+                txn.appArgs = txnForEnc.apaa.map(arg => new Uint8Array(arg));
             }
             if (txnForEnc.apat !== undefined) {
-                txn.appAccounts = [];
-                txnForEnc.apat.forEach((addressBytes) => {
-                   txn.appAccounts.push(address.decodeAddress(address.encodeAddress(new Uint8Array(addressBytes))));
-                });
+                txn.appAccounts = txnForEnc.apat.map(addressBytes => address.decodeAddress(address.encodeAddress(new Uint8Array(addressBytes))));
             }
             if (txnForEnc.apfa !== undefined) {
                 txn.appForeignApps = txnForEnc.apfa;
diff --git a/tests/5.Transaction.js b/tests/5.Transaction.js
index 7615a8e12..bef2fad6d 100644
--- a/tests/5.Transaction.js
+++ b/tests/5.Transaction.js
@@ -5,6 +5,36 @@ const algosdk = require('../index');
 const group = require('../src/group');
 
 describe('Sign', function () {
+    it('should not modify input arrays', function () {
+        const appArgs = [Uint8Array.from([1, 2]), Uint8Array.from([3, 4])];
+        const appAccounts = ["7ZUECA7HFLZTXENRV24SHLU4AVPUTMTTDUFUBNBD64C73F3UHRTHAIOF6Q", "UCE2U2JC4O4ZR6W763GUQCG57HQCDZEUJY4J5I6VYY4HQZUJDF7AKZO5GM"];
+        const appForeignApps = [17, 200];
+        const appForeignAssets = [7, 8, 9];
+        const o = {
+            "from": "7ZUECA7HFLZTXENRV24SHLU4AVPUTMTTDUFUBNBD64C73F3UHRTHAIOF6Q",
+            "fee": 10,
+            "firstRound": 51,
+            "lastRound": 61,
+            "genesisHash": "JgsgCaCTqIaLeVhyL6XlRu3n7Rfk2FxMeK+wRSaQ7dI=",
+            "note": new Uint8Array(0),
+            "type": "appl",
+            "appIndex": 5,
+            "appArgs": appArgs,
+            "appAccounts": appAccounts,
+            "appForeignApps": appForeignApps,
+            "appForeignAssets": appForeignAssets,
+        };
+        const txn = new algosdk.Transaction(o);
+        assert.deepStrictEqual(appArgs, [Uint8Array.from([1, 2]), Uint8Array.from([3, 4])]);
+        assert.deepStrictEqual(appAccounts, ["7ZUECA7HFLZTXENRV24SHLU4AVPUTMTTDUFUBNBD64C73F3UHRTHAIOF6Q", "UCE2U2JC4O4ZR6W763GUQCG57HQCDZEUJY4J5I6VYY4HQZUJDF7AKZO5GM"]);
+        assert.deepStrictEqual(appForeignApps, [17, 200]);
+        assert.deepStrictEqual(appForeignAssets, [7, 8, 9]);
+        assert.ok(txn.appArgs !== appArgs);
+        assert.ok(txn.appAccounts !== appAccounts);
+        assert.ok(txn.appForeignApps !== appForeignApps);
+        assert.ok(txn.appForeignAssets !== appForeignAssets);
+    });
+
     it('should not complain on a missing note', function () {
         let o = {
             "from": "7ZUECA7HFLZTXENRV24SHLU4AVPUTMTTDUFUBNBD64C73F3UHRTHAIOF6Q",