diff --git a/src/account/account.cpp b/src/account/account.cpp
index 7ab6bd2..777a933 100644
--- a/src/account/account.cpp
+++ b/src/account/account.cpp
@@ -21,7 +21,7 @@ Account::Account()
 	GenerateAddressesFromPrivateKey();
 }
 
-Account::Account(uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE])
+Account::Account(const uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE])
 {
 	setDepsFromGlobals();
 	// Copy the private key
@@ -30,7 +30,7 @@ Account::Account(uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE])
 }
 
 Account::Account(Random* pRandomGenerator, Encoder* pEncoder, Signer* pSigner,
-				 uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE])
+				 const uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE])
 {
 	_pRandomGenerator = pRandomGenerator;
 	_pSigner = pSigner;
diff --git a/src/account/account.h b/src/account/account.h
index b9b4b47..0a1bff2 100644
--- a/src/account/account.h
+++ b/src/account/account.h
@@ -26,7 +26,7 @@ class Account
 	 *
 	 * @param privateKey The private key
 	 */
-	Account(uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE]);
+	Account(const uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE]);
 
 	/**************************************************************************/
 	/* Getters */
@@ -217,7 +217,7 @@ class Account
   public:
 	// Allow to inject mock dependencies in constructor
 	Account(Random* pRandomGenerator, Encoder* pEncoder, Signer* pSigner,
-			uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE] = nullptr);
+			const uint8_t privateKey[IOTEX_PRIVATE_KEY_SIZE] = nullptr);
 };
 } // namespace iotex
 
diff --git a/src/contract/xrc20Contract.cpp b/src/contract/xrc20Contract.cpp
index 6501c95..570d3a9 100644
--- a/src/contract/xrc20Contract.cpp
+++ b/src/contract/xrc20Contract.cpp
@@ -9,7 +9,7 @@ void Xrc20Contract::generateCallDataForTotalSupply(uint8_t data[4])
 	memcpy(data, functionSelector, sizeof(functionSelector));
 }
 
-void Xrc20Contract::generateCallDataForBalanceOf(uint8_t address[ETH_ADDRESS_SIZE],
+void Xrc20Contract::generateCallDataForBalanceOf(const uint8_t address[ETH_ADDRESS_SIZE],
 												 uint8_t data[36])
 {
 	uint8_t* it = data;
@@ -19,7 +19,7 @@ void Xrc20Contract::generateCallDataForBalanceOf(uint8_t address[ETH_ADDRESS_SIZ
 	Contract::generateBytesForAddress(address, it);
 }
 
-void Xrc20Contract::generateCallDataForTransfer(uint8_t to[ETH_ADDRESS_SIZE], uint64_t value,
+void Xrc20Contract::generateCallDataForTransfer(const uint8_t to[ETH_ADDRESS_SIZE], uint64_t value,
 												uint8_t data[68])
 {
 	uint8_t* it = data;
diff --git a/src/contract/xrc20Contract.h b/src/contract/xrc20Contract.h
index 019a9be..148d703 100644
--- a/src/contract/xrc20Contract.h
+++ b/src/contract/xrc20Contract.h
@@ -28,7 +28,7 @@ class Xrc20Contract
 	 * @param address The ethereum address
 	 * @param[out] data The buffere where the data is stored
 	 */
-	static void generateCallDataForBalanceOf(uint8_t address[ETH_ADDRESS_SIZE],
+	static void generateCallDataForBalanceOf(const uint8_t address[ETH_ADDRESS_SIZE],
 											 uint8_t data[IOTEX_CONTRACT_ENCODED_TOTALSUPPLY_SIZE]);
 
 	/**
@@ -39,7 +39,7 @@ class Xrc20Contract
 	 * @param value The amount to transfer
 	 * @param data
 	 */
-	static void generateCallDataForTransfer(uint8_t to[ETH_ADDRESS_SIZE], uint64_t value,
+	static void generateCallDataForTransfer(const uint8_t to[ETH_ADDRESS_SIZE], uint64_t value,
 											uint8_t data[IOTEX_CONTRACT_ENCODED_TRANSFER_SIZE]);
 };
 } // namespace iotex