diff --git a/cadquery/assembly.py b/cadquery/assembly.py
index 1aac2cb3d..cc6cfe806 100644
--- a/cadquery/assembly.py
+++ b/cadquery/assembly.py
@@ -218,7 +218,9 @@ def add(self, arg, **kwargs):
             # enforce unique names
             name = kwargs["name"] if kwargs.get("name") else arg.name
             if name in self.objects:
-                raise ValueError("Unique name is required")
+                raise ValueError(
+                    f"Unique name is required. {name} is already in the assembly"
+                )
 
             subassy = arg._copy()