diff --git a/masque/repetition.py b/masque/repetition.py
index 0426c08..867adf7 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -64,7 +64,7 @@ class Grid(Repetition):
     _a_count: int
     """ Number of instances along the direction specified by the `a_vector` """
 
-    _b_vector: NDArray[numpy.float64] | None
+    _b_vector: NDArray[numpy.float64]
     """ Vector `[x, y]` specifying a second lattice vector for the grid.
         Specifies center-to-center spacing between adjacent elements.
         Can be `None` for a 1D array.
@@ -199,9 +199,6 @@ class Grid(Repetition):
 
     @property
     def displacements(self) -> NDArray[numpy.float64]:
-        if self.b_vector is None:
-            return numpy.arange(self.a_count)[:, None] * self.a_vector[None, :]
-
         aa, bb = numpy.meshgrid(numpy.arange(self.a_count), numpy.arange(self.b_count), indexing='ij')
         return (aa.flatten()[:, None] * self.a_vector[None, :]
               + bb.flatten()[:, None] * self.b_vector[None, :])             # noqa