diff --git a/include/ip.h b/include/ip.h
index c23f96a..9c3a653 100644
--- a/include/ip.h
+++ b/include/ip.h
@@ -364,6 +364,17 @@ namespace Tins {
         /**
          * \brief Setter for the protocol field.
          *
+         * Note that this protocol will be overwritten using the 
+         * inner_pdu's protocol type during serialization unless the IP 
+         * datagram is fragmented. 
+         * 
+         * If the packet is fragmented and was originally sniffed, the
+         * original protocol type will be kept when serialized.
+         * 
+         * If this packet has been crafted manually and the inner_pdu
+         * is, for example, a RawPDU, then setting the protocol yourself
+         * is necessary.
+         * 
          * \param new_protocol The new protocol.
          */
         void protocol(uint8_t new_protocol);
diff --git a/src/ip.cpp b/src/ip.cpp
index 28a43b8..bd9301e 100644
--- a/src/ip.cpp
+++ b/src/ip.cpp
@@ -400,8 +400,8 @@ void IP::write_serialization(uint8_t *buffer, uint32_t total_sz, const PDU* pare
                 Internals::pdu_type_to_id<IP>(inner_pdu()->pdu_type())
             );
         }
-        protocol(new_flag);
-        //flag(new_flag);
+        if(!is_fragmented() || new_flag != 0xff)
+            protocol(new_flag);
     }
     
     #if __FreeBSD__ || defined(__FreeBSD_kernel__)
diff --git a/tests/src/ip.cpp b/tests/src/ip.cpp
index 272a5ec..b15e85c 100644
--- a/tests/src/ip.cpp
+++ b/tests/src/ip.cpp
@@ -8,13 +8,14 @@
 #include "icmp.h"
 #include "ip_address.h"
 #include "utils.h"
+#include "ethernetII.h"
 
 using namespace std;
 using namespace Tins;
 
 class IPTest : public testing::Test {
 public:
-    static const uint8_t expected_packet[], fragmented_packet[];
+    static const uint8_t expected_packet[], fragmented_packet[], fragmented_ether_ip_packet[];
     
     void test_equals(const IP &ip1, const IP &ip2);
 };
@@ -30,6 +31,13 @@ const uint8_t IPTest::fragmented_packet[] = {
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
 };
 
+const uint8_t IPTest::fragmented_ether_ip_packet[] = {
+    0, 10, 94, 83, 216, 229, 0, 21, 197, 50, 245, 6, 8, 0, 69, 0, 0, 60, 
+    0, 242, 7, 223, 64, 17, 237, 220, 192, 0, 2, 1, 192, 0, 2, 2, 192, 0, 
+    192, 0, 0, 40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
 
 TEST_F(IPTest, DefaultConstructor) {
     IP ip;
@@ -75,6 +83,18 @@ TEST_F(IPTest, ConstructorFromFragmentedPacket) {
     EXPECT_EQ(PDU::RAW, ip.inner_pdu()->pdu_type());
 }
 
+TEST_F(IPTest, SerializeFragmentedPacket) {
+    EthernetII pkt(fragmented_ether_ip_packet, sizeof(fragmented_ether_ip_packet));
+    PDU::serialization_type buffer = pkt.serialize();
+    EXPECT_EQ(
+        PDU::serialization_type(
+            fragmented_ether_ip_packet, 
+            fragmented_ether_ip_packet + sizeof(fragmented_ether_ip_packet)
+        ),
+        buffer
+    );
+}
+
 TEST_F(IPTest, TOS) {
     IP ip;
     ip.tos(0x7a);