diff --git a/include/udp.h b/include/udp.h
index c0cbfa7..6afd89b 100644
--- a/include/udp.h
+++ b/include/udp.h
@@ -91,13 +91,15 @@ namespace Tins {
          */
         void dport(uint16_t new_dport);
 
-        /** \brief Set the source port.
+        /** 
+         * \brief Set the source port.
          *
          * \param new_sport The new source port.
          */
         void sport(uint16_t new_sport);
         
-        /** \brief Getter for the length field.
+        /** 
+         * \brief Getter for the length field.
          * \param new_len The new length field.
          * \return The length field.
          */
@@ -115,7 +117,8 @@ namespace Tins {
          */
         bool matches_response(uint8_t *ptr, uint32_t total_sz);
 
-        /** \brief Returns the header size.
+        /** 
+         * \brief Returns the header size.
          *
          * This metod overrides PDU::header_size. This size includes the
          * payload and options size. \sa PDU::header_size
diff --git a/src/udp.cpp b/src/udp.cpp
index 057578f..7b7549d 100644
--- a/src/udp.cpp
+++ b/src/udp.cpp
@@ -77,19 +77,24 @@ void UDP::write_serialization(uint8_t *buffer, uint32_t total_sz, const PDU *par
     assert(total_sz >= sizeof(udphdr));
     #endif
     const Tins::IP *ip_packet = dynamic_cast<const Tins::IP*>(parent);
+    _udp.check = 0;
     if(inner_pdu())
         length(sizeof(udphdr) + inner_pdu()->size());
     else
         length(sizeof(udphdr));
     std::memcpy(buffer, &_udp, sizeof(udphdr));
-    if(!_udp.check && ip_packet) {
-        uint32_t checksum = Utils::pseudoheader_checksum(ip_packet->src_addr(), ip_packet->dst_addr(), size(), Constants::IP::PROTO_UDP) +
-                            Utils::do_checksum(buffer, buffer + total_sz);
+    if(ip_packet) {
+        uint32_t checksum = Utils::pseudoheader_checksum(
+                                ip_packet->src_addr(), 
+                                ip_packet->dst_addr(), 
+                                size(), 
+                                Constants::IP::PROTO_UDP
+                            ) + Utils::do_checksum(buffer, buffer + total_sz);
         while (checksum >> 16)
             checksum = (checksum & 0xffff)+(checksum >> 16);
-        ((udphdr*)buffer)->check = Endian::host_to_be<uint16_t>(~checksum);
+        _udp.check = Endian::host_to_be<uint16_t>(~checksum);
+        ((udphdr*)buffer)->check = _udp.check;
     }
-    _udp.check = 0;
 }
 
 bool UDP::matches_response(uint8_t *ptr, uint32_t total_sz) {
diff --git a/tests/src/ip.cpp b/tests/src/ip.cpp
index 6ac0284..d67fc38 100644
--- a/tests/src/ip.cpp
+++ b/tests/src/ip.cpp
@@ -20,7 +20,7 @@ public:
 };
 
 const uint8_t IPTest::expected_packet[] = { 
-    40, 127, 0, 32, 0, 122, 0, 67, 21, 1, 251, 103, 84, 52, 254, 5, 192, 
+    40, 127, 0, 32, 0, 122, 0, 67, 21, 1, 0, 0, 84, 52, 254, 5, 192, 
     168, 9, 43, 130, 11, 116, 106, 103, 171, 119, 171, 104, 101, 108, 0
 };