diff --git a/src/icmp.cpp b/src/icmp.cpp
index 9b4c9c2..0ce0242 100644
--- a/src/icmp.cpp
+++ b/src/icmp.cpp
@@ -57,10 +57,14 @@ ICMP::ICMP(const uint8_t *buffer, uint32_t total_sz)
     buffer += sizeof(icmphdr);
     total_sz -= sizeof(icmphdr);
     if(type() == TIMESTAMP_REQUEST || type() == TIMESTAMP_REPLY) {
+        if(total_sz < sizeof(uint32_t) * 3)
+            throw malformed_packet();
         const uint32_t *ptr = reinterpret_cast<const uint32_t*>(buffer);
         original_timestamp(*ptr++);
         receive_timestamp(*ptr++);
         transmit_timestamp(*ptr++);
+        total_sz -= sizeof(uint32_t) * 3;
+        buffer += sizeof(uint32_t) * 3;
     }
     if(total_sz)
         inner_pdu(new RawPDU(buffer, total_sz));
@@ -183,17 +187,16 @@ void ICMP::write_serialization(uint8_t *buffer, uint32_t total_sz, const PDU *)
         *ptr++ = receive_timestamp();
         *ptr++ = transmit_timestamp();
     }
-
     // checksum calc
     _icmp.check = 0;
-    
-    uint32_t checksum = Utils::do_checksum(buffer + ICMP::header_size(), buffer + total_sz) + 
-                        Utils::do_checksum((uint8_t*)&_icmp, ((uint8_t*)&_icmp) + ICMP::header_size());
+    memcpy(buffer, &_icmp, sizeof(icmphdr));
+    uint32_t checksum = Utils::do_checksum(buffer, buffer + total_sz);
+
     while (checksum >> 16)
         checksum = (checksum & 0xffff) + (checksum >> 16);
 
     _icmp.check = Endian::host_to_be<uint16_t>(~checksum);
-    memcpy(buffer, &_icmp, sizeof(icmphdr));
+    ((icmphdr*)buffer)->check = _icmp.check;
 }
 
 bool ICMP::matches_response(const uint8_t *ptr, uint32_t total_sz) const {
diff --git a/tests/src/icmp.cpp b/tests/src/icmp.cpp
index 7754f20..2b73850 100644
--- a/tests/src/icmp.cpp
+++ b/tests/src/icmp.cpp
@@ -3,6 +3,8 @@
 #include <string>
 #include <stdint.h>
 #include "icmp.h"
+#include "ip.h"
+#include "ethernetII.h"
 #include "utils.h"
 
 using namespace std;
@@ -67,6 +69,19 @@ TEST_F(ICMPTest, FlagConstructor) {
     EXPECT_EQ(icmp.type(), ICMP::ECHO_REPLY);
 }
 
+TEST_F(ICMPTest, ChecksumOnTimestamp) {
+    const uint8_t raw_pkt[] = {
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 0, 69, 0, 0, 45, 0, 1, 0, 
+        0, 128, 1, 185, 25, 192, 168, 0, 100, 192, 168, 0, 1, 13, 0, 237, 
+        141, 0, 0, 0, 0, 159, 134, 1, 0, 151, 134, 1, 0, 152, 134, 1, 0, 
+        98, 111, 105, 110, 103, 0
+    };
+    EthernetII pkt(raw_pkt, sizeof(raw_pkt));
+    pkt.serialize();
+    EXPECT_EQ(0xb919, pkt.rfind_pdu<IP>().checksum());
+    EXPECT_EQ(0xed8d, pkt.rfind_pdu<ICMP>().check());
+}
+
 TEST_F(ICMPTest, Code) {
     ICMP icmp;
     icmp.code(0x7a);