diff --git a/src/build123d/build_common.py b/src/build123d/build_common.py
index 97b0ce9..4621f95 100644
--- a/src/build123d/build_common.py
+++ b/src/build123d/build_common.py
@@ -263,7 +263,7 @@ class Builder(ABC, Generic[ShapeT]):
         # by CPython in Linux, Window & MacOS but may not be supported in other python
         # implementations.  Support outside of these OS's is outside the scope of this
         # project.
-        builder_context = Builder._get_context()
+        builder_context : Builder[ShapeT] | None = Builder._get_context()
         current_frame = inspect.currentframe()
         same_scope = (
             builder_context._python_frame == current_Frame.f_back