diff --git a/src/base58.h b/src/base58.h
index 7fefbc5d..90ce34b0 100644
--- a/src/base58.h
+++ b/src/base58.h
@@ -288,7 +288,7 @@ public:
 
     bool IsValid() const
     {
-        int nExpectedSize = 20;
+        unsigned int nExpectedSize = 20;
         bool fExpectTestNet = false;
         switch(nVersion)
         {
diff --git a/src/crypter.cpp b/src/crypter.cpp
index 83041add..2501305e 100644
--- a/src/crypter.cpp
+++ b/src/crypter.cpp
@@ -31,7 +31,7 @@ bool CCrypter::SetKeyFromPassphrase(const SecureString& strKeyData, const std::v
         i = EVP_BytesToKey(EVP_aes_256_cbc(), EVP_sha512(), &chSalt[0],
                           (unsigned char *)&strKeyData[0], strKeyData.size(), nRounds, chKey, chIV);
 
-    if (i != WALLET_CRYPTO_KEY_SIZE)
+    if (i != (int)WALLET_CRYPTO_KEY_SIZE)
     {
         memset(&chKey, 0, sizeof chKey);
         memset(&chIV, 0, sizeof chIV);
diff --git a/src/key.h b/src/key.h
index b8fc0cd7..8f220f1c 100644
--- a/src/key.h
+++ b/src/key.h
@@ -173,7 +173,7 @@ public:
 
     CPrivKey GetPrivKey() const
     {
-        unsigned int nSize = i2d_ECPrivateKey(pkey, NULL);
+        int nSize = i2d_ECPrivateKey(pkey, NULL);
         if (!nSize)
             throw key_error("CKey::GetPrivKey() : i2d_ECPrivateKey failed");
         CPrivKey vchPrivKey(nSize, 0);
@@ -196,7 +196,7 @@ public:
 
     std::vector<unsigned char> GetPubKey() const
     {
-        unsigned int nSize = i2o_ECPublicKey(pkey, NULL);
+        int nSize = i2o_ECPublicKey(pkey, NULL);
         if (!nSize)
             throw key_error("CKey::GetPubKey() : i2o_ECPublicKey failed");
         std::vector<unsigned char> vchPubKey(nSize, 0);