diff --git a/proxy/http/remap/UrlRewrite.cc b/proxy/http/remap/UrlRewrite.cc
index fcd4f39ae14..e2ec415526a 100644
--- a/proxy/http/remap/UrlRewrite.cc
+++ b/proxy/http/remap/UrlRewrite.cc
@@ -769,7 +769,8 @@ UrlRewrite::TableInsert(std::unique_ptr<URLTable> &h_table, url_mapping *mapping
     h_table->emplace(src_host, ht_contents);
   }
   if (!ht_contents->Insert(mapping)) {
-    Warning("Could not insert new mapping");
+    // Trie::Insert only fails due to an attempt to add a duplicate entry.
+    Warning("Could not insert new mapping: duplicated entry exists");
     return false;
   }
   return true;