diff --git a/src/cli/cli_dataset.cpp b/src/cli/cli_dataset.cpp
index f4dbaa365..347acd767 100644
--- a/src/cli/cli_dataset.cpp
+++ b/src/cli/cli_dataset.cpp
@@ -589,7 +589,7 @@ ThreadError Dataset::ProcessMgmtGetCommand(otInstance *aInstance, int argc, char
         else if (strcmp(argv[index], "binary") == 0)
         {
             VerifyOrExit((index + 1) < argc, error = kThreadError_Parse);
-            value = (strlen(argv[++index]) + 1) / 2;
+            value = static_cast<long>(strlen(argv[++index]) + 1) / 2;
             VerifyOrExit(static_cast<size_t>(value) <= (sizeof(tlvs) - static_cast<size_t>(length)), error = kThreadError_NoBufs);
             VerifyOrExit(Interpreter::Hex2Bin(argv[index], tlvs + length, static_cast<uint16_t>(value)) >= 0,
                          error = kThreadError_Parse);
diff --git a/src/core/coap/coap_header.cpp b/src/core/coap/coap_header.cpp
index 0849ce8de..0570dd4e8 100644
--- a/src/core/coap/coap_header.cpp
+++ b/src/core/coap/coap_header.cpp
@@ -147,7 +147,7 @@ ThreadError Header::FromMessage(const Message &aMessage)
 
         VerifyOrExit(optionLength <= length, error = kThreadError_Parse);
         aMessage.Read(offset, optionLength, mHeader + mHeaderLength);
-        mHeaderLength += optionLength;
+        mHeaderLength += static_cast<uint8_t>(optionLength);
         offset += optionLength;
         length -= optionLength;
     }
@@ -200,7 +200,7 @@ ThreadError Header::AppendOption(const Option &aOption)
     memcpy(cur, aOption.mValue, aOption.mLength);
     cur += aOption.mLength;
 
-    mHeaderLength += cur - buf;
+    mHeaderLength += static_cast<uint8_t>(cur - buf);
     mOptionLast = aOption.mNumber;
 
     return kThreadError_None;
@@ -232,7 +232,7 @@ ThreadError Header::AppendUriPathOptions(const char *aUriPath)
 ThreadError Header::AppendContentFormatOption(MediaType aType)
 {
     Option coapOption;
-    uint8_t type = aType;
+    uint8_t type = static_cast<uint8_t>(aType);
 
     coapOption.mNumber = Option::kOptionContentFormat;
     coapOption.mLength = 1;
diff --git a/src/core/coap/coap_header.hpp b/src/core/coap/coap_header.hpp
index 687e58641..93388dc6e 100644
--- a/src/core/coap/coap_header.hpp
+++ b/src/core/coap/coap_header.hpp
@@ -157,7 +157,7 @@ public:
      * @param[in]  aCode  The Code value.
      *
      */
-    void SetCode(Code aCode) { mCode = aCode; }
+    void SetCode(Code aCode) { mCode = static_cast<uint8_t>(aCode); }
 
     /**
      * This method returns the Message ID value.
diff --git a/src/core/common/message.cpp b/src/core/common/message.cpp
index 486b065b6..2bdce33a1 100644
--- a/src/core/common/message.cpp
+++ b/src/core/common/message.cpp
@@ -201,7 +201,7 @@ ThreadError Message::MoveOffset(int aDelta)
     assert(GetOffset() + aDelta <= GetLength());
     VerifyOrExit(GetOffset() + aDelta <= GetLength(), error = kThreadError_InvalidArgs);
 
-    mInfo.mOffset += aDelta;
+    mInfo.mOffset += static_cast<uint16_t>(aDelta);
     assert(mInfo.mOffset <= GetLength());
 
 exit:
diff --git a/src/core/meshcop/dtls.cpp b/src/core/meshcop/dtls.cpp
index d4d9f15d3..2593157e8 100644
--- a/src/core/meshcop/dtls.cpp
+++ b/src/core/meshcop/dtls.cpp
@@ -178,7 +178,7 @@ int Dtls::HandleMbedtlsTransmit(void *aContext, const unsigned char *aBuf, size_
 int Dtls::HandleMbedtlsTransmit(const unsigned char *aBuf, size_t aLength)
 {
     ThreadError error;
-    int rval;
+    int rval = 0;
 
     otLogInfoMeshCoP("Dtls::HandleMbedtlsTransmit\r\n");
 
@@ -221,8 +221,8 @@ int Dtls::HandleMbedtlsReceive(unsigned char *aBuf, size_t aLength)
     }
 
     rval = (int)mReceiveMessage->Read(mReceiveOffset, (uint16_t)aLength, aBuf);
-    mReceiveOffset += rval;
-    mReceiveLength -= rval;
+    mReceiveOffset += static_cast<uint16_t>(rval);
+    mReceiveLength -= static_cast<uint16_t>(rval);
 
 exit:
     return rval;
@@ -351,7 +351,7 @@ void Dtls::Process(void)
 
 ThreadError Dtls::MapError(int rval)
 {
-    ThreadError error;
+    ThreadError error = kThreadError_None;
 
     switch (rval)
     {
@@ -364,15 +364,7 @@ ThreadError Dtls::MapError(int rval)
         break;
 
     default:
-        if (rval >= 0)
-        {
-            error = kThreadError_None;
-        }
-        else
-        {
-            assert(false);
-        }
-
+        assert(rval >= 0);
         break;
     }
 
diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index add9a5982..f9325c812 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -100,7 +100,7 @@ uint16_t Ip6::ComputePseudoheaderChecksum(const Address &src, const Address &dst
     uint16_t checksum;
 
     checksum = Ip6::UpdateChecksum(0, length);
-    checksum = Ip6::UpdateChecksum(checksum, proto);
+    checksum = Ip6::UpdateChecksum(checksum, static_cast<uint16_t>(proto));
     checksum = UpdateChecksum(checksum, src);
     checksum = UpdateChecksum(checksum, dst);
 
@@ -323,7 +323,7 @@ ThreadError Ip6::HandleExtensionHeaders(Message &message, uint8_t &nextHeader, b
             ExitNow();
         }
 
-        nextHeader = extensionHeader.GetNextHeader();
+        nextHeader = static_cast<uint8_t>(extensionHeader.GetNextHeader());
     }
 
 exit:
@@ -485,7 +485,7 @@ ThreadError Ip6::HandleDatagram(Message &message, Netif *netif, int8_t interface
     message.SetOffset(sizeof(header));
 
     // process IPv6 Extension Headers
-    nextHeader = header.GetNextHeader();
+    nextHeader = static_cast<uint8_t>(header.GetNextHeader());
     SuccessOrExit(error = HandleExtensionHeaders(message, nextHeader, receive));
 
     // process IPv6 Payload
diff --git a/src/core/net/ip6_mpl.hpp b/src/core/net/ip6_mpl.hpp
index 43030e6ad..02831c280 100644
--- a/src/core/net/ip6_mpl.hpp
+++ b/src/core/net/ip6_mpl.hpp
@@ -99,7 +99,7 @@ public:
      * @param[in]  aSeedLength  The MPL Seed Length.
      *
      */
-    void SetSeedLength(SeedLength aSeedLength) { mControl = (mControl & ~kSeedLengthMask) | aSeedLength; }
+    void SetSeedLength(SeedLength aSeedLength) { mControl = static_cast<uint8_t>((mControl & ~kSeedLengthMask) | aSeedLength); }
 
     /**
      * This method indicates whether or not the MPL M flag is set.
diff --git a/src/core/thread/lowpan.cpp b/src/core/thread/lowpan.cpp
index dc0ef93fb..b6da543f5 100644
--- a/src/core/thread/lowpan.cpp
+++ b/src/core/thread/lowpan.cpp
@@ -288,7 +288,7 @@ int Lowpan::Compress(Message &aMessage, const Mac::Address &aMacSource, const Ma
         break;
 
     default:
-        cur[0] = ip6Header.GetNextHeader();
+        cur[0] = static_cast<uint8_t>(ip6Header.GetNextHeader());
         cur++;
         break;
     }
@@ -358,7 +358,7 @@ int Lowpan::Compress(Message &aMessage, const Mac::Address &aMacSource, const Ma
     aBuf[1] = hcCtl & 0xff;
     aMessage.SetOffset(sizeof(ip6Header));
 
-    nextHeader = ip6Header.GetNextHeader();
+    nextHeader = static_cast<uint8_t>(ip6Header.GetNextHeader());
 
     while (1)
     {
@@ -391,7 +391,7 @@ int Lowpan::CompressExtensionHeader(Message &aMessage, uint8_t *aBuf, uint8_t &a
     aMessage.MoveOffset(sizeof(extHeader));
 
     cur[0] = kExtHdrDispatch | kExtHdrEidHbh;
-    aNextHeader = extHeader.GetNextHeader();
+    aNextHeader = static_cast<uint8_t>(extHeader.GetNextHeader());
 
     switch (extHeader.GetNextHeader())
     {
@@ -401,7 +401,7 @@ int Lowpan::CompressExtensionHeader(Message &aMessage, uint8_t *aBuf, uint8_t &a
 
     default:
         cur++;
-        cur[0] = extHeader.GetNextHeader();
+        cur[0] = static_cast<uint8_t>(extHeader.GetNextHeader());
         break;
     }
 
diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index cb0ab15de..2e3fd2663 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -850,7 +850,7 @@ ThreadError MeshForwarder::SendFragment(Message &aMessage, Mac::Frame &aFrame)
     if (aMessage.IsLinkSecurityEnabled())
     {
         fcf |= Mac::Frame::kFcfSecurityEnabled;
-        secCtl = aMessage.IsJoinerEntrust() ? Mac::Frame::kKeyIdMode0 : Mac::Frame::kKeyIdMode1;
+        secCtl = static_cast<uint8_t>(aMessage.IsJoinerEntrust() ? Mac::Frame::kKeyIdMode0 : Mac::Frame::kKeyIdMode1);
         secCtl |= Mac::Frame::kSecEncMic32;
     }
 
@@ -911,7 +911,7 @@ ThreadError MeshForwarder::SendFragment(Message &aMessage, Mac::Frame &aFrame)
     {
         hcLength = mLowpan.Compress(aMessage, meshSource, meshDest, payload);
         assert(hcLength > 0);
-        headerLength += hcLength;
+        headerLength += static_cast<uint8_t>(hcLength);
 
         payloadLength = aMessage.GetLength() - aMessage.GetOffset();
 
@@ -1309,7 +1309,7 @@ void MeshForwarder::HandleFragment(uint8_t *aFrame, uint8_t aFrameLength,
         VerifyOrExit(headerLength > 0, error = kThreadError_NoBufs);
 
         aFrame += headerLength;
-        aFrameLength -= headerLength;
+        aFrameLength -= static_cast<uint8_t>(headerLength);
 
         VerifyOrExit(message->SetLength(datagramLength) == kThreadError_None, error = kThreadError_NoBufs);
         datagramLength = HostSwap16(datagramLength - sizeof(Ip6::Header));
@@ -1422,7 +1422,7 @@ void MeshForwarder::HandleLowpanHC(uint8_t *aFrame, uint8_t aFrameLength,
     VerifyOrExit(headerLength > 0, error = kThreadError_Drop);
 
     aFrame += headerLength;
-    aFrameLength -= headerLength;
+    aFrameLength -= static_cast<uint8_t>(headerLength);
 
     SuccessOrExit(error = message->SetLength(message->GetLength() + aFrameLength));
 
diff --git a/src/core/thread/meshcop_dataset_manager.cpp b/src/core/thread/meshcop_dataset_manager.cpp
index dab2a5094..2163c753f 100644
--- a/src/core/thread/meshcop_dataset_manager.cpp
+++ b/src/core/thread/meshcop_dataset_manager.cpp
@@ -245,7 +245,8 @@ void DatasetManager::HandleSet(Coap::Header &aHeader, Message &aMessage, const I
 
     VerifyOrExit(mMle.GetDeviceState() == Mle::kDeviceStateLeader, state = StateTlv::kReject);
 
-    type = strcmp(mUriSet, OPENTHREAD_URI_ACTIVE_SET) == 0 ? Tlv::kActiveTimestamp : Tlv::kPendingTimestamp;
+    type = static_cast<uint8_t>(strcmp(mUriSet,
+                                       OPENTHREAD_URI_ACTIVE_SET) == 0 ? Tlv::kActiveTimestamp : Tlv::kPendingTimestamp);
 
     while (offset < aMessage.GetLength())
     {
diff --git a/src/ncp/spinel.c b/src/ncp/spinel.c
index 420236677..10cffc340 100644
--- a/src/ncp/spinel.c
+++ b/src/ncp/spinel.c
@@ -393,9 +393,9 @@ spinel_datatype_vunpack_(const uint8_t *data_ptr, spinel_size_t data_len, const
                 *arg_ptr = (const char *)data_ptr;
             }
 
-            ret += len;
+            ret += (spinel_size_t)len;
             data_ptr += len;
-            data_len -= len;
+            data_len -= (spinel_size_t)len;
             break;
         }
 
@@ -719,14 +719,14 @@ spinel_datatype_vpack_(uint8_t *data_ptr, spinel_size_t data_len_max, const char
                 string_arg_len = 1;
             }
 
-            ret += string_arg_len;
+            ret += (spinel_size_t)string_arg_len;
 
             if (data_len_max >= string_arg_len)
             {
                 memcpy(data_ptr, string_arg, string_arg_len);
 
                 data_ptr += string_arg_len;
-                data_len_max -= string_arg_len;
+                data_len_max -= (spinel_size_t)string_arg_len;
             }
             else
             {
diff --git a/tests/unit/test_vector.c b/tests/unit/test_vector.c
index 5f1c253b7..69a1df06e 100644
--- a/tests/unit/test_vector.c
+++ b/tests/unit/test_vector.c
@@ -28,7 +28,7 @@
 
 #include "test_vector.h"
 
-const test_lowpan_vector_t sTestVectorLowpan[] =
+test_lowpan_vector_t sTestVectorLowpan[] =
 {
     {
         // I1_t1_AF_pass.pcap
diff --git a/tests/unit/test_vector.h b/tests/unit/test_vector.h
index 999dabc26..eea110e85 100644
--- a/tests/unit/test_vector.h
+++ b/tests/unit/test_vector.h
@@ -64,7 +64,7 @@ typedef const struct
 } test_lowpan_vector_t;
 
 
-extern const test_lowpan_vector_t sTestVectorLowpan[];
+extern test_lowpan_vector_t sTestVectorLowpan[];
 extern const unsigned sTestVectorLowpanLen;
 
 #ifdef __cplusplus