diff --git a/src/Add-on/Join.ts b/src/Add-on/Join.ts
index 9aa2f6671..a582deace 100644
--- a/src/Add-on/Join.ts
+++ b/src/Add-on/Join.ts
@@ -81,7 +81,9 @@ export class Command_Join implements Command
                 pl.Join(cu);
                 cu.Erase();
             }
-            app.m_Database.ModelSpace.Append(pl);
+
+            if (pl.Id === undefined)
+                app.m_Database.ModelSpace.Append(pl);
         }
     }