diff --git a/src/lib/asiodns/tests/io_fetch_unittest.cc b/src/lib/asiodns/tests/io_fetch_unittest.cc
index e93e796ae9..7b4cd0568e 100644
--- a/src/lib/asiodns/tests/io_fetch_unittest.cc
+++ b/src/lib/asiodns/tests/io_fetch_unittest.cc
@@ -290,7 +290,7 @@ public:
         if (cumulative_ > 2) {
             uint16_t dns_length = readUint16(receive_buffer_,
                                              sizeof(receive_buffer_));
-            complete = ((dns_length + 2) == cumulative_);
+            complete = ((static_cast<size_t>(dns_length) + 2) == cumulative_);
         }
 
         if (!complete) {
diff --git a/src/lib/dhcp/option_data_types.cc b/src/lib/dhcp/option_data_types.cc
index 24a4fbd789..1d581e6771 100644
--- a/src/lib/dhcp/option_data_types.cc
+++ b/src/lib/dhcp/option_data_types.cc
@@ -211,7 +211,7 @@ OptionDataTypeUtil::readTuple(const std::vector<uint8_t>& buf,
                       << buf.size());
         }
         uint8_t len = buf[0];
-        if (buf.size() < 1 + len) {
+        if (buf.size() < 1 + static_cast<size_t>(len)) {
             isc_throw(BadDataTypeCast, "unable to read data from the buffer as"
                       << " tuple (length " << static_cast<unsigned>(len)
                       << "). Invalid buffer size: " << buf.size());
@@ -227,7 +227,7 @@ OptionDataTypeUtil::readTuple(const std::vector<uint8_t>& buf,
                       << buf.size());
         }
         uint16_t len = isc::util::readUint16(&buf[0], 2);
-        if (buf.size() < 2 + len) {
+        if (buf.size() < 2 + static_cast<size_t>(len)) {
             isc_throw(BadDataTypeCast, "unable to read data from the buffer as"
                       << " tuple (length " << len
                       << "). Invalid buffer size: " << buf.size());
diff --git a/src/lib/dns/char_string.cc b/src/lib/dns/char_string.cc
index 25cb1f180f..30a99455d5 100644
--- a/src/lib/dns/char_string.cc
+++ b/src/lib/dns/char_string.cc
@@ -239,7 +239,7 @@ bufferToCharString(isc::util::InputBuffer& buffer, size_t rdata_len,
                   "insufficient data to read character-string length");
     }
     const uint8_t len = buffer.readUint8();
-    if (rdata_len < len + 1) {
+    if (rdata_len < static_cast<size_t>(len) + 1) {
         isc_throw(isc::dns::DNSMessageFORMERR,
                   "character string length is too large: " <<
                   static_cast<int>(len));
diff --git a/src/lib/dns/labelsequence.cc b/src/lib/dns/labelsequence.cc
index bbdc71ca58..1d68c9fe86 100644
--- a/src/lib/dns/labelsequence.cc
+++ b/src/lib/dns/labelsequence.cc
@@ -134,7 +134,7 @@ LabelSequence::serialize(void* buf, size_t buf_len) const {
     bp += ndata_len;
 
     isc_throw_assert(bp - reinterpret_cast<const uint8_t*>(buf) ==
-                     static_cast<const ssize_t>(expected_size));
+                     static_cast<ssize_t>(expected_size));
 }
 
 bool
diff --git a/src/lib/dns/tests/time_utils_unittest.cc b/src/lib/dns/tests/time_utils_unittest.cc
index 320b6ceea7..40a0baa276 100644
--- a/src/lib/dns/tests/time_utils_unittest.cc
+++ b/src/lib/dns/tests/time_utils_unittest.cc
@@ -73,8 +73,8 @@ TEST_F(DNSSECTimeTest, fromText) {
 
     // On the other hand, the 64-bit version should return monotonically
     // increasing counters.
-    EXPECT_EQ(4294967296LL, timeFromText64("21060207062816"));
-    EXPECT_EQ(4294967306LL, timeFromText64("21060207062826"));
+    EXPECT_EQ(4294967296LLU, timeFromText64("21060207062816"));
+    EXPECT_EQ(4294967306LLU, timeFromText64("21060207062826"));
 }
 
 // This helper templated function tells timeToText32 a faked current time.
@@ -144,4 +144,4 @@ TEST_F(DNSSECTimeTest, overflow) {
     EXPECT_THROW(timeToText32(4294197632LU), InvalidTime);
 }
 
-}  // namespace
\ No newline at end of file
+}  // namespace
diff --git a/src/lib/dns/txt_like.h b/src/lib/dns/txt_like.h
index f88b1a6a6e..7492f85db7 100644
--- a/src/lib/dns/txt_like.h
+++ b/src/lib/dns/txt_like.h
@@ -52,7 +52,7 @@ public:
 
         do {
             const uint8_t len = buffer.readUint8();
-            if (rdata_len < len + 1) {
+            if (rdata_len < static_cast<size_t>(len) + 1) {
                 isc_throw(DNSMessageFORMERR, "Error in parsing " <<
                           RRType(typeCode) <<
                           " RDATA: character string length is too large: " <<