diff --git a/src/ip.cpp b/src/ip.cpp
index eb646f7..f1d6bfc 100644
--- a/src/ip.cpp
+++ b/src/ip.cpp
@@ -385,7 +385,7 @@ void IP::write_serialization(uint8_t *buffer, uint32_t total_sz, const PDU* pare
                 Internals::pdu_type_to_id<IP>(inner_pdu()->pdu_type())
             );
         }
-        if(!is_fragmented() || new_flag != 0xff)
+        if(!is_fragmented() && new_flag != 0xff)
             protocol(new_flag);
     }