diff --git a/web3.js/module.flow.js b/web3.js/module.flow.js
index 8c430d2ea..e71bda5e8 100644
--- a/web3.js/module.flow.js
+++ b/web3.js/module.flow.js
@@ -19,7 +19,6 @@ declare module '@solana/web3.js' {
     constructor(
       value: number | string | Buffer | Uint8Array | Array<number>,
     ): PublicKey;
-    static isPublicKey(o: {}): boolean;
     static createWithSeed(
       fromPublicKey: PublicKey,
       seed: string,
diff --git a/web3.js/src/publickey.js b/web3.js/src/publickey.js
index 51c1d716c..bd1d0fda2 100644
--- a/web3.js/src/publickey.js
+++ b/web3.js/src/publickey.js
@@ -35,13 +35,6 @@ export class PublicKey {
     }
   }
 
-  /**
-   * Checks if the provided object is a PublicKey
-   */
-  static isPublicKey(o: Object): boolean {
-    return o instanceof PublicKey;
-  }
-
   /**
    * Checks if two publicKeys are equal
    */
diff --git a/web3.js/src/transaction.js b/web3.js/src/transaction.js
index 7f0802f8b..1219503f5 100644
--- a/web3.js/src/transaction.js
+++ b/web3.js/src/transaction.js
@@ -177,10 +177,10 @@ export class Transaction {
       throw new Error('No instructions');
     }
 
-    items.forEach(item => {
-      if (item instanceof Transaction) {
+    items.forEach((item: any) => {
+      if ('instructions' in item) {
         this.instructions = this.instructions.concat(item.instructions);
-      } else if (item instanceof TransactionInstruction) {
+      } else if ('data' in item && 'programId' in item && 'keys' in item) {
         this.instructions.push(item);
       } else {
         this.instructions.push(new TransactionInstruction(item));
@@ -366,31 +366,39 @@ export class Transaction {
     if (partialSigners.length === 0) {
       throw new Error('No signers');
     }
+
+    function partialSignerPublicKey(accountOrPublicKey: any): PublicKey {
+      if ('publicKey' in accountOrPublicKey) {
+        return accountOrPublicKey.publicKey;
+      }
+      return accountOrPublicKey;
+    }
+
+    function signerAccount(accountOrPublicKey: any): ?Account {
+      if (
+        'publicKey' in accountOrPublicKey &&
+        'secretKey' in accountOrPublicKey
+      ) {
+        return accountOrPublicKey;
+      }
+    }
+
     const signatures: Array<SignaturePubkeyPair> = partialSigners.map(
-      accountOrPublicKey => {
-        const publicKey =
-          accountOrPublicKey instanceof Account
-            ? accountOrPublicKey.publicKey
-            : accountOrPublicKey;
-        return {
-          signature: null,
-          publicKey,
-        };
-      },
+      accountOrPublicKey => ({
+        signature: null,
+        publicKey: partialSignerPublicKey(accountOrPublicKey),
+      }),
     );
     this.signatures = signatures;
     const signData = this.serializeMessage();
 
     partialSigners.forEach((accountOrPublicKey, index) => {
-      if (accountOrPublicKey instanceof PublicKey) {
-        return;
+      const account = signerAccount(accountOrPublicKey);
+      if (account) {
+        const signature = nacl.sign.detached(signData, account.secretKey);
+        invariant(signature.length === 64);
+        signatures[index].signature = Buffer.from(signature);
       }
-      const signature = nacl.sign.detached(
-        signData,
-        accountOrPublicKey.secretKey,
-      );
-      invariant(signature.length === 64);
-      signatures[index].signature = Buffer.from(signature);
     });
   }
 
diff --git a/web3.js/test/account.test.js b/web3.js/test/account.test.js
index d54bbdd89..89c37f6ba 100644
--- a/web3.js/test/account.test.js
+++ b/web3.js/test/account.test.js
@@ -1,10 +1,8 @@
 // @flow
 import {Account} from '../src/account';
-import {PublicKey} from '../src/publickey';
 
 test('generate new account', () => {
   const account = new Account();
-  expect(PublicKey.isPublicKey(account.publicKey)).toBeTruthy();
   expect(account.secretKey).toHaveLength(64);
 });
 
diff --git a/web3.js/test/publickey.test.js b/web3.js/test/publickey.test.js
index 7cc87bdda..bfa638adc 100644
--- a/web3.js/test/publickey.test.js
+++ b/web3.js/test/publickey.test.js
@@ -103,14 +103,6 @@ test('equals', () => {
   expect(arrayKey.equals(base56Key)).toBe(true);
 });
 
-test('isPublicKey', () => {
-  const key = new PublicKey(
-    '0x100000000000000000000000000000000000000000000000000000000000000',
-  );
-  expect(PublicKey.isPublicKey(key)).toBe(true);
-  expect(PublicKey.isPublicKey({})).toBe(false);
-});
-
 test('toBase58', () => {
   const key = new PublicKey(
     '0x300000000000000000000000000000000000000000000000000000000000000',