diff --git a/src/core/border_router/routing_manager.cpp b/src/core/border_router/routing_manager.cpp
index 576a87ee4..58bae226c 100644
--- a/src/core/border_router/routing_manager.cpp
+++ b/src/core/border_router/routing_manager.cpp
@@ -845,8 +845,6 @@ bool RoutingManager::IsValidOnLinkPrefix(const Ip6::Nd::PrefixInfoOption &aPio)
 
 bool RoutingManager::IsValidOnLinkPrefix(const Ip6::Prefix &aOnLinkPrefix)
 {
-    static constexpr uint8_t kOnLinkPrefixLength = 64;
-
     return (aOnLinkPrefix.GetLength() == kOnLinkPrefixLength) && !aOnLinkPrefix.IsLinkLocal() &&
            !aOnLinkPrefix.IsMulticast();
 }