diff --git a/lns.go b/lns.go
index 04d7832..ca18ce1 100644
--- a/lns.go
+++ b/lns.go
@@ -301,6 +301,12 @@ func (s *Service) LockedSize() int {
 	return s.LockedCatalog().Size()
 }
 
+// LockedPrefixSize reports the byte offset where locked-name entries begin in
+// the reference table.
+func (s *Service) LockedPrefixSize() int {
+	return s.LockedCatalog().PrefixSize()
+}
+
 // LockedEntries exposes the locked-name catalog entries used by the service.
 func (s *Service) LockedEntries() []covenant.LockedEntry {
 	return s.LockedCatalog().Entries()
diff --git a/lns_test.go b/lns_test.go
index 65d4fb3..ea4bd05 100644
--- a/lns_test.go
+++ b/lns_test.go
@@ -493,6 +493,10 @@ func TestServiceLockedCatalog(t *testing.T) {
 		t.Fatalf("LockedSize() = %d, want %d", got, catalog.Size())
 	}
 
+	if got := svc.LockedPrefixSize(); got != catalog.PrefixSize() {
+		t.Fatalf("LockedPrefixSize() = %d, want %d", got, catalog.PrefixSize())
+	}
+
 	if !catalog.HasByName("NEC") {
 		t.Fatal("LockedCatalog should expose the locked catalog helpers")
 	}
diff --git a/pkg/covenant/locked_lookup.go b/pkg/covenant/locked_lookup.go
index 3358d72..e151407 100644
--- a/pkg/covenant/locked_lookup.go
+++ b/pkg/covenant/locked_lookup.go
@@ -38,6 +38,8 @@ type LockedEntry struct {
 	Value LockedName
 }
 
+const lockedCatalogPrefixSize = 4
+
 var (
 	lockedCatalogOnce sync.Once
 	lockedCatalog     *LockedCatalog
@@ -87,6 +89,11 @@ func (c *LockedCatalog) Size() int {
 	return len(c.byHash)
 }
 
+// PrefixSize reports the byte offset where the locked-name table entries begin.
+func (c *LockedCatalog) PrefixSize() int {
+	return lockedCatalogPrefixSize
+}
+
 // Has reports whether the catalog contains the hash.
 func (c *LockedCatalog) Has(hash primitives.Hash) bool {
 	if c == nil {
diff --git a/pkg/covenant/locked_lookup_test.go b/pkg/covenant/locked_lookup_test.go
index c6f277f..8250368 100644
--- a/pkg/covenant/locked_lookup_test.go
+++ b/pkg/covenant/locked_lookup_test.go
@@ -89,6 +89,10 @@ func TestLockedCatalogHelpers(t *testing.T) {
 		t.Fatal("catalog should report a non-zero size")
 	}
 
+	if catalog.PrefixSize() != lockedCatalogPrefixSize {
+		t.Fatalf("catalog.PrefixSize() = %d, want %d", catalog.PrefixSize(), lockedCatalogPrefixSize)
+	}
+
 	if !catalog.HasByName("NEC") {
 		t.Fatal("catalog should find names case-insensitively")
 	}