diff --git a/gprMax/grid.py b/gprMax/grid.py
index 4fc295c5..8dd6ded4 100644
--- a/gprMax/grid.py
+++ b/gprMax/grid.py
@@ -497,5 +497,5 @@ def Iz(x, y, z, Hx, Hy, Hz, G):
     return Iz
 
 
-class GPUGrid(Grid):
+class GPUGrid(FDTDGrid):
     pass