diff --git a/src/core/thread/mesh_forwarder.hpp b/src/core/thread/mesh_forwarder.hpp
index 30db918b0..5730d87a3 100644
--- a/src/core/thread/mesh_forwarder.hpp
+++ b/src/core/thread/mesh_forwarder.hpp
@@ -544,7 +544,7 @@ private:
     void  SendMesh(Message &aMessage, Mac::TxFrame &aFrame);
     void  SendDestinationUnreachable(uint16_t aMeshSource, const Ip6::Headers &aIp6Headers);
     Error UpdateIp6Route(Message &aMessage);
-    Error UpdateIp6RouteFtd(Ip6::Header &ip6Header, Message &aMessage);
+    Error UpdateIp6RouteFtd(const Ip6::Header &aIp6Header, Message &aMessage);
     void  EvaluateRoutingCost(uint16_t aDest, uint8_t &aBestCost, uint16_t &aBestDest) const;
     Error AnycastRouteLookup(uint8_t aServiceId, AnycastType aType, uint16_t &aMeshDest) const;
     Error UpdateMeshRoute(Message &aMessage);
diff --git a/src/core/thread/mesh_forwarder_ftd.cpp b/src/core/thread/mesh_forwarder_ftd.cpp
index d77da246b..e46ff7e0d 100644
--- a/src/core/thread/mesh_forwarder_ftd.cpp
+++ b/src/core/thread/mesh_forwarder_ftd.cpp
@@ -497,7 +497,7 @@ exit:
     return (bestDest != Mac::kShortAddrInvalid) ? kErrorNone : kErrorNoRoute;
 }
 
-Error MeshForwarder::UpdateIp6RouteFtd(Ip6::Header &ip6Header, Message &aMessage)
+Error MeshForwarder::UpdateIp6RouteFtd(const Ip6::Header &aIp6Header, Message &aMessage)
 {
     Mle::MleRouter &mle   = Get<Mle::MleRouter>();
     Error           error = kErrorNone;
@@ -507,15 +507,15 @@ Error MeshForwarder::UpdateIp6RouteFtd(Ip6::Header &ip6Header, Message &aMessage
     {
         mMeshDest = aMessage.GetMeshDest();
     }
-    else if (mle.IsRoutingLocator(ip6Header.GetDestination()))
+    else if (mle.IsRoutingLocator(aIp6Header.GetDestination()))
     {
-        uint16_t rloc16 = ip6Header.GetDestination().GetIid().GetLocator();
+        uint16_t rloc16 = aIp6Header.GetDestination().GetIid().GetLocator();
         VerifyOrExit(mle.IsRouterIdValid(Mle::RouterIdFromRloc16(rloc16)), error = kErrorDrop);
         mMeshDest = rloc16;
     }
-    else if (mle.IsAnycastLocator(ip6Header.GetDestination()))
+    else if (mle.IsAnycastLocator(aIp6Header.GetDestination()))
     {
-        uint16_t aloc16 = ip6Header.GetDestination().GetIid().GetLocator();
+        uint16_t aloc16 = aIp6Header.GetDestination().GetIid().GetLocator();
 
         if (aloc16 == Mle::kAloc16Leader)
         {
@@ -554,25 +554,25 @@ Error MeshForwarder::UpdateIp6RouteFtd(Ip6::Header &ip6Header, Message &aMessage
             ExitNow(error = kErrorDrop);
         }
     }
-    else if ((neighbor = Get<NeighborTable>().FindNeighbor(ip6Header.GetDestination())) != nullptr)
+    else if ((neighbor = Get<NeighborTable>().FindNeighbor(aIp6Header.GetDestination())) != nullptr)
     {
         mMeshDest = neighbor->GetRloc16();
     }
-    else if (Get<NetworkData::Leader>().IsOnMesh(ip6Header.GetDestination()))
+    else if (Get<NetworkData::Leader>().IsOnMesh(aIp6Header.GetDestination()))
     {
-        SuccessOrExit(error = Get<AddressResolver>().Resolve(ip6Header.GetDestination(), mMeshDest));
+        SuccessOrExit(error = Get<AddressResolver>().Resolve(aIp6Header.GetDestination(), mMeshDest));
     }
     else
     {
         IgnoreError(
-            Get<NetworkData::Leader>().RouteLookup(ip6Header.GetSource(), ip6Header.GetDestination(), mMeshDest));
+            Get<NetworkData::Leader>().RouteLookup(aIp6Header.GetSource(), aIp6Header.GetDestination(), mMeshDest));
     }
 
     VerifyOrExit(mMeshDest != Mac::kShortAddrInvalid, error = kErrorDrop);
 
     mMeshSource = Get<Mac::Mac>().GetShortAddress();
 
-    SuccessOrExit(error = mle.CheckReachability(mMeshDest, ip6Header));
+    SuccessOrExit(error = mle.CheckReachability(mMeshDest, aIp6Header));
     aMessage.SetMeshDest(mMeshDest);
     mMacAddrs.mDestination.SetShort(mle.GetNextHop(mMeshDest));
 
diff --git a/src/core/thread/mle_router.hpp b/src/core/thread/mle_router.hpp
index 21fe0f95b..1ac8d195e 100644
--- a/src/core/thread/mle_router.hpp
+++ b/src/core/thread/mle_router.hpp
@@ -785,7 +785,7 @@ public:
 
     Error SendChildUpdateRequest(void) { return Mle::SendChildUpdateRequest(); }
 
-    Error CheckReachability(uint16_t aMeshDest, Ip6::Header &aIp6Header)
+    Error CheckReachability(uint16_t aMeshDest, const Ip6::Header &aIp6Header)
     {
         return Mle::CheckReachability(aMeshDest, aIp6Header);
     }