diff --git a/openmc/lattice.py b/openmc/lattice.py
index f7f9da8ea8..5180685605 100644
--- a/openmc/lattice.py
+++ b/openmc/lattice.py
@@ -884,6 +884,10 @@ class RectLattice(Lattice):
         dimension = ET.SubElement(lattice_subelement, "dimension")
         dimension.text = ' '.join(map(str, self.shape))
 
+        # Make sure lower_left has been specified
+        if self.lower_left is None:
+            raise ValueError(f"Lattice {self.id} does not have lower_left specified.")
+
         # Export Lattice lower left
         lower_left = ET.SubElement(lattice_subelement, "lower_left")
         lower_left.text = ' '.join(map(str, self._lower_left))