diff --git a/src/core/thread/network_data.cpp b/src/core/thread/network_data.cpp
index 0813c7c1a..4bdd6509b 100644
--- a/src/core/thread/network_data.cpp
+++ b/src/core/thread/network_data.cpp
@@ -211,7 +211,7 @@ otError NetworkData::GetNextExternalRoute(otNetworkDataIterator *aIterator, uint
         aConfig->mRloc16 = hasRouteEntry->GetRloc();
         aConfig->mNextHopIsThisDevice = (hasRouteEntry->GetRloc() == GetNetif().GetMle().GetRloc16());
 
-        *aIterator = static_cast<otNetworkDataIterator>(reinterpret_cast<uint8_t *>(cur->GetNext()) - mTlvs);
+        iterator.SetTlvsIndex(static_cast<uint8_t>(reinterpret_cast<uint8_t *>(cur) - mTlvs));
 
         ExitNow(error = OT_ERROR_NONE);
     }