diff --git a/src/util/name_set.cpp b/src/util/name_set.cpp
index 0ea3568ee..820d8f6e4 100644
--- a/src/util/name_set.cpp
+++ b/src/util/name_set.cpp
@@ -18,6 +18,13 @@ name mk_unique(name_set const & s, name const & suggestion) {
     }
 }
 
+name_set to_name_set(buffer<name> const & ns) {
+    name_set r;
+    for (name const & n : ns)
+        r.insert(n);
+    return r;
+}
+
 DECL_UDATA(name_set)
 static int mk_name_set(lua_State * L) {
     name_set r;
diff --git a/src/util/name_set.h b/src/util/name_set.h
index d1cfcc0af..e032f904a 100644
--- a/src/util/name_set.h
+++ b/src/util/name_set.h
@@ -13,6 +13,8 @@ typedef rb_tree<name, name_quick_cmp> name_set;
 /** \brief Make a name that does not occur in \c s, based on the given suggestion. */
 name mk_unique(name_set const & s, name const & suggestion);
 
+name_set to_name_set(buffer<name> const & ns);
+
 UDATA_DEFS_CORE(name_set)
 void open_name_set(lua_State * L);
 }