diff --git a/galgebra/lt.py b/galgebra/lt.py
index 857bf9fc..4529659b 100644
--- a/galgebra/lt.py
+++ b/galgebra/lt.py
@@ -362,7 +362,7 @@ def __init__(self, *args, ga, f=False, mode='g'):
             self.lt_dict = {}
             for base in self.Ga.basis:
                 out = F(mv.Mv(base, ga=self.Ga))
-                if not out.is_vector():
+                if not out.is_vector() and not out.is_zero():
                     raise ValueError('{} must return vectors'.format(F))
                 self.lt_dict[base] = out.obj
         else: