diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index 82fda68a6..c6f028c0f 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -1219,22 +1219,21 @@ Error Ip6::HandleDatagram(OwnedPtr<Message> aMessagePtr, bool aIsReassembled)
             SuccessOrExit(error);
         }
 
-        if (aMessagePtr->IsOriginHostUntrusted() && (nextHeader == kProtoUdp))
-        {
-            uint16_t destPort;
-
-            SuccessOrExit(
-                error = aMessagePtr->Read(aMessagePtr->GetOffset() + Udp::Header::kDestPortFieldOffset, destPort));
-            destPort = BigEndian::HostSwap16(destPort);
-
-            if (destPort == Tmf::kUdpPort
 #if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
-                && mTmfOriginFilterEnabled
+        if (mTmfOriginFilterEnabled)
 #endif
-            )
+        {
+            if (aMessagePtr->IsOriginHostUntrusted() && (nextHeader == kProtoUdp))
             {
-                LogNote("Dropping TMF message from untrusted origin");
-                ExitNow(error = kErrorDrop);
+                Udp::Header udpHeader;
+
+                SuccessOrExit(error = aMessagePtr->Read(aMessagePtr->GetOffset(), udpHeader));
+
+                if (udpHeader.GetDestinationPort() == Tmf::kUdpPort)
+                {
+                    LogNote("Dropping TMF message from untrusted origin");
+                    ExitNow(error = kErrorDrop);
+                }
             }
         }