diff --git a/eth/main.cpp b/eth/main.cpp
index 461494cef..db6acbbca 100644
--- a/eth/main.cpp
+++ b/eth/main.cpp
@@ -364,7 +364,7 @@ int main(int argc, char** argv)
 			{
 				coinbase = h160(fromHex(argv[++i], WhenError::Throw));
 			}
-			catch (BadHexCharacter& _e)
+			catch (BadHexCharacter&)
 			{
 				cerr << "Bad hex in " << arg << " option: " << argv[i] << endl;
 				return -1;
diff --git a/libdevcore/CommonData.h b/libdevcore/CommonData.h
index 38ccd71f0..93bad71a3 100644
--- a/libdevcore/CommonData.h
+++ b/libdevcore/CommonData.h
@@ -116,9 +116,9 @@ inline void toBigEndian(_T _val, _Out& o_out)
 template <class _T, class _In>
 inline _T fromBigEndian(_In const& _bytes)
 {
-	_T ret = 0;
+	_T ret = (_T)0;
 	for (auto i: _bytes)
-		ret = (ret << 8) | (byte)(typename std::make_unsigned<typename _In::value_type>::type)i;
+		ret = (_T)((ret << 8) | (byte)(typename std::make_unsigned<typename _In::value_type>::type)i);
 	return ret;
 }
 
diff --git a/libethash/ethash.h b/libethash/ethash.h
index 7594fc835..bc62a29cc 100644
--- a/libethash/ethash.h
+++ b/libethash/ethash.h
@@ -85,7 +85,7 @@ typedef uint8_t const ethash_seedhash_t[32];
 
 typedef void const* ethash_light_t;
 static inline ethash_light_t ethash_new_light(ethash_params const* params, ethash_seedhash_t seed) {
-	void* ret = malloc(params->cache_size);
+	void* ret = malloc((size_t)params->cache_size);
 	ethash_mkcache(ret, params, seed);
 	return ret;
 }
@@ -98,7 +98,7 @@ static inline void ethash_delete_light(ethash_light_t light) {
 
 typedef void const* ethash_full_t;
 static inline ethash_full_t ethash_new_full(ethash_params const* params, ethash_light_t light) {
-	void* ret = malloc(params->full_size);
+	void* ret = malloc((size_t)params->full_size);
 	ethash_compute_full_data(ret, params, light);
 	return ret;
 }
diff --git a/libethash/io.c b/libethash/io.c
index 0e935fa59..07387caaf 100644
--- a/libethash/io.c
+++ b/libethash/io.c
@@ -61,13 +61,13 @@ bool ethash_io_write(char const *dirname,
 {
     char info_buffer[DAG_MEMO_BYTESIZE];
     // allocate the bytes
-    uint8_t *temp_data_ptr = malloc(params->full_size);
+	uint8_t *temp_data_ptr = malloc((size_t)params->full_size);
     if (!temp_data_ptr) {
         goto end;
     }
     ethash_compute_full_data(temp_data_ptr, params, cache);
 
-    if (!ethash_io_write_file(dirname, PASS_ARR(DAG_FILE_NAME), temp_data_ptr, params->full_size)) {
+	if (!ethash_io_write_file(dirname, PASS_ARR(DAG_FILE_NAME), temp_data_ptr, (size_t)params->full_size)) {
         goto fail_free;
     }
 
@@ -77,7 +77,7 @@ bool ethash_io_write(char const *dirname,
     }
 
     *data = temp_data_ptr;
-    *data_size = params->full_size;
+	*data_size = (size_t)params->full_size;
     return true;
 
 fail_free:
diff --git a/libethcore/Ethash.cpp b/libethcore/Ethash.cpp
index 3dd9d3b60..a777205e9 100644
--- a/libethcore/Ethash.cpp
+++ b/libethcore/Ethash.cpp
@@ -48,7 +48,7 @@ namespace dev
 namespace eth
 {
 
-const Ethash::WorkPackage Ethash::NullWorkPackage;
+const Ethash::WorkPackage Ethash::NullWorkPackage = Ethash::WorkPackage();
 
 std::string Ethash::name()
 {
@@ -81,7 +81,7 @@ bool Ethash::preVerify(BlockInfo const& _header)
 
 	h256 boundary = u256((bigint(1) << 256) / _header.difficulty);
 
-	return ethash_quick_check_difficulty(
+	return !!ethash_quick_check_difficulty(
 		_header.headerHash(WithoutNonce).data(),
 		(uint64_t)(u64)_header.nonce,
 		_header.mixHash.data(),
diff --git a/mix/ContractCallDataEncoder.cpp b/mix/ContractCallDataEncoder.cpp
index 56aeb1d34..e1f02f631 100644
--- a/mix/ContractCallDataEncoder.cpp
+++ b/mix/ContractCallDataEncoder.cpp
@@ -118,7 +118,7 @@ unsigned ContractCallDataEncoder::encodeSingleItem(QString const& _data, Solidit
 			result = bytes(alignSize);
 			toBigEndian((u256)i, result);
 		}
-		catch (std::exception const& ex)
+		catch (std::exception const&)
 		{
 			// manage input as a string.
 			QByteArray bytesAr = src.toLocal8Bit();