diff --git a/masque/builder/pather_mixin.py b/masque/builder/pather_mixin.py
index 180f451..4cb8ce9 100644
--- a/masque/builder/pather_mixin.py
+++ b/masque/builder/pather_mixin.py
@@ -410,7 +410,7 @@ class PatherMixin(metaclass=ABCMeta):
         for bt in ('emin', 'emax', 'pmin', 'pmax', 'xmin', 'xmax', 'ymin', 'ymax', 'min_past_furthest'):
             if bt in kwargs:
                 bound_types.add(bt)
-                bound = kwargs.pop('bt')
+                bound = kwargs.pop(bt)
 
         if not bound_types:
             raise BuildError('No bound type specified for mpath')