diff --git a/src/crypto/aes.h b/src/crypto/aes.h
index 08ec2b795..174d10cf3 100644
--- a/src/crypto/aes.h
+++ b/src/crypto/aes.h
@@ -1,114 +1,114 @@
 // Copyright (c) 2015-2016 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 //
 // C++ wrapper around ctaes, a constant-time AES implementation
 
 #ifndef BITCOIN_CRYPTO_AES_H
 #define BITCOIN_CRYPTO_AES_H
 
 extern "C" {
 #include "crypto/ctaes/ctaes.h"
 }
 
 static const int AES_BLOCKSIZE = 16;
 static const int AES128_KEYSIZE = 16;
 static const int AES256_KEYSIZE = 32;
 
 /** An encryption class for AES-128. */
 class AES128Encrypt {
 private:
     AES128_ctx ctx;
 
 public:
-    AES128Encrypt(const uint8_t key[16]);
+    explicit AES128Encrypt(const uint8_t key[16]);
     ~AES128Encrypt();
     void Encrypt(uint8_t ciphertext[16], const uint8_t plaintext[16]) const;
 };
 
 /** A decryption class for AES-128. */
 class AES128Decrypt {
 private:
     AES128_ctx ctx;
 
 public:
-    AES128Decrypt(const uint8_t key[16]);
+    explicit AES128Decrypt(const uint8_t key[16]);
     ~AES128Decrypt();
     void Decrypt(uint8_t plaintext[16], const uint8_t ciphertext[16]) const;
 };
 
 /** An encryption class for AES-256. */
 class AES256Encrypt {
 private:
     AES256_ctx ctx;
 
 public:
-    AES256Encrypt(const uint8_t key[32]);
+    explicit AES256Encrypt(const uint8_t key[32]);
     ~AES256Encrypt();
     void Encrypt(uint8_t ciphertext[16], const uint8_t plaintext[16]) const;
 };
 
 /** A decryption class for AES-256. */
 class AES256Decrypt {
 private:
     AES256_ctx ctx;
 
 public:
-    AES256Decrypt(const uint8_t key[32]);
+    explicit AES256Decrypt(const uint8_t key[32]);
     ~AES256Decrypt();
     void Decrypt(uint8_t plaintext[16], const uint8_t ciphertext[16]) const;
 };
 
 class AES256CBCEncrypt {
 public:
-    AES256CBCEncrypt(const uint8_t key[AES256_KEYSIZE],
-                     const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
+    explicit AES256CBCEncrypt(const uint8_t key[AES256_KEYSIZE],
+                              const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
     ~AES256CBCEncrypt();
     int Encrypt(const uint8_t *data, int size, uint8_t *out) const;
 
 private:
     const AES256Encrypt enc;
     const bool pad;
     uint8_t iv[AES_BLOCKSIZE];
 };
 
 class AES256CBCDecrypt {
 public:
-    AES256CBCDecrypt(const uint8_t key[AES256_KEYSIZE],
-                     const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
+    explicit AES256CBCDecrypt(const uint8_t key[AES256_KEYSIZE],
+                              const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
     ~AES256CBCDecrypt();
     int Decrypt(const uint8_t *data, int size, uint8_t *out) const;
 
 private:
     const AES256Decrypt dec;
     const bool pad;
     uint8_t iv[AES_BLOCKSIZE];
 };
 
 class AES128CBCEncrypt {
 public:
-    AES128CBCEncrypt(const uint8_t key[AES128_KEYSIZE],
-                     const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
+    explicit AES128CBCEncrypt(const uint8_t key[AES128_KEYSIZE],
+                              const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
     ~AES128CBCEncrypt();
     int Encrypt(const uint8_t *data, int size, uint8_t *out) const;
 
 private:
     const AES128Encrypt enc;
     const bool pad;
     uint8_t iv[AES_BLOCKSIZE];
 };
 
 class AES128CBCDecrypt {
 public:
-    AES128CBCDecrypt(const uint8_t key[AES128_KEYSIZE],
-                     const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
+    explicit AES128CBCDecrypt(const uint8_t key[AES128_KEYSIZE],
+                              const uint8_t ivIn[AES_BLOCKSIZE], bool padIn);
     ~AES128CBCDecrypt();
     int Decrypt(const uint8_t *data, int size, uint8_t *out) const;
 
 private:
     const AES128Decrypt dec;
     const bool pad;
     uint8_t iv[AES_BLOCKSIZE];
 };
 
 #endif // BITCOIN_CRYPTO_AES_H