diff --git a/test/msgpack_cpp11.cpp b/test/msgpack_cpp11.cpp
index 8a6fa95a..d69af910 100644
--- a/test/msgpack_cpp11.cpp
+++ b/test/msgpack_cpp11.cpp
@@ -887,7 +887,7 @@ TEST(MSGPACK_CHRONO, system_clock_32)
     msgpack::sbuffer sbuf;
     msgpack::pack(sbuf, val1);
     char packed[] = {
-        static_cast<char>(0xd6),
+        static_cast<char>(0xd6u),
         static_cast<char>(-1),
         static_cast<char>(0x12),
         static_cast<char>(0x34),
@@ -912,12 +912,12 @@ TEST(MSGPACK_CHRONO, system_clock_32_max)
     msgpack::sbuffer sbuf;
     msgpack::pack(sbuf, val1);
     char packed[] = {
-        static_cast<char>(0xd6),
+        static_cast<char>(0xd6u),
         static_cast<char>(-1),
-        static_cast<char>(0xff),
-        static_cast<char>(0xff),
-        static_cast<char>(0xff),
-        static_cast<char>(0xff)
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu)
     };
     EXPECT_EQ(memcmp(sbuf.data(), packed, sizeof(packed)), 0);
 
@@ -963,28 +963,28 @@ TEST(MSGPACK_CHRONO, system_clock_64_max)
     msgpack::sbuffer sbuf;
     msgpack::pack(sbuf, val1);
     char packed_nano[] = {
-        static_cast<char>(0xd7),
+        static_cast<char>(0xd7u),
         static_cast<char>(-1),
-        static_cast<char>(0xee), // 999,999,999 << 2
+        static_cast<char>(0xeeu), // 999,999,999 << 2
         static_cast<char>(0x6b),
         static_cast<char>(0x27),
-        static_cast<char>(0xfc),
-        static_cast<char>(0xff), // 32 bit sec
-        static_cast<char>(0xff),
-        static_cast<char>(0xff),
-        static_cast<char>(0xff)
+        static_cast<char>(0xfcu),
+        static_cast<char>(0xffu), // 32 bit sec
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu)
     };
     char packed_micro[] = {
-        static_cast<char>(0xd7),
+        static_cast<char>(0xd7u),
         static_cast<char>(-1),
-        static_cast<char>(0xee), // 999,999,000 << 2
+        static_cast<char>(0xeeu), // 999,999,000 << 2
         static_cast<char>(0x6b),
         static_cast<char>(0x18),
         static_cast<char>(0x60),
-        static_cast<char>(0xff), // 32 bit sec
-        static_cast<char>(0xff),
-        static_cast<char>(0xff),
-        static_cast<char>(0xff)
+        static_cast<char>(0xffu), // 32 bit sec
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu),
+        static_cast<char>(0xffu)
     };
     if (std::chrono::system_clock::duration::period::ratio::den == 1000000000) {
         EXPECT_EQ(memcmp(sbuf.data(), packed_nano, sizeof(packed_nano)), 0);
@@ -1060,7 +1060,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_zero)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xd6));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xd6u));
 
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
@@ -1086,7 +1086,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_32bit_sec)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xd6));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xd6u));
 
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
@@ -1112,7 +1112,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_max_nano)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xd7));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xd7u));
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
     timespec val2 = oh.get().as<timespec>();
@@ -1138,7 +1138,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_34bit_sec_max_nano)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xd7));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xd7u));
 
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
@@ -1166,7 +1166,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_35bit_sec_max_nano)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xc7));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xc7u));
 
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
@@ -1193,7 +1193,7 @@ TEST(MSGPACK_TIMESPEC, timespec_pack_convert_64bit_sec_max_nano)
 
     msgpack::pack(ss, val1);
     std::string const& str = ss.str();
-    EXPECT_EQ(str.data()[0], static_cast<char>(0xc7));
+    EXPECT_EQ(str.data()[0], static_cast<char>(0xc7u));
 
     msgpack::object_handle oh;
     msgpack::unpack(oh, str.data(), str.size());
diff --git a/test/pack_unpack.cpp b/test/pack_unpack.cpp
index 6bc119fc..28dd27b4 100644
--- a/test/pack_unpack.cpp
+++ b/test/pack_unpack.cpp
@@ -528,7 +528,7 @@ TEST(unpack, int_off_larger_than_length)
 TEST(unpack, empty_array_fix)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0x90));
+    buf.push_back(static_cast<char>(0x90u));
     std::size_t off = 0;
 
     msgpack::object_handle oh = msgpack::unpack(buf.data(), buf.size(), off);
@@ -540,7 +540,7 @@ TEST(unpack, empty_array_fix)
 TEST(unpack, empty_array_16)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0xdc));
+    buf.push_back(static_cast<char>(0xdcu));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));
     std::size_t off = 0;
@@ -554,7 +554,7 @@ TEST(unpack, empty_array_16)
 TEST(unpack, empty_array_32)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0xdd));
+    buf.push_back(static_cast<char>(0xddu));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));
@@ -570,7 +570,7 @@ TEST(unpack, empty_array_32)
 TEST(unpack, empty_map_fix)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0x80));
+    buf.push_back(static_cast<char>(0x80u));
     std::size_t off = 0;
 
     msgpack::object_handle oh = msgpack::unpack(buf.data(), buf.size(), off);
@@ -582,7 +582,7 @@ TEST(unpack, empty_map_fix)
 TEST(unpack, empty_map_16)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0xde));
+    buf.push_back(static_cast<char>(0xdeu));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));
     std::size_t off = 0;
@@ -596,7 +596,7 @@ TEST(unpack, empty_map_16)
 TEST(unpack, empty_map_32)
 {
     std::string buf;
-    buf.push_back(static_cast<char>(0xdf));
+    buf.push_back(static_cast<char>(0xdfu));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));
     buf.push_back(static_cast<char>(0x00));