diff --git a/src/core/border_router/routing_manager.cpp b/src/core/border_router/routing_manager.cpp
index 6283e73d2..2973b269f 100644
--- a/src/core/border_router/routing_manager.cpp
+++ b/src/core/border_router/routing_manager.cpp
@@ -1906,6 +1906,7 @@ exit:
 
 void RoutingManager::DiscoveredPrefixTable::Entry::InitFrom(const Ip6::Nd::RouterAdvertMessage::Header &aRaHeader)
 {
+    mPrefix.Clear();
     mType                    = kTypeRoute;
     mValidLifetime           = aRaHeader.GetRouterLifetime();
     mShared.mRoutePreference = aRaHeader.GetDefaultRouterPreference();