diff --git a/opencl_fdtd/simulation.py b/opencl_fdtd/simulation.py
index d24dcf2..1e573c9 100644
--- a/opencl_fdtd/simulation.py
+++ b/opencl_fdtd/simulation.py
@@ -166,7 +166,7 @@ class Simulation(object):
         ctype = type_to_C(self.arg_type)
 
         def ptr(arg: str) -> str:
-            return ctype + ' *' + arg
+            return ctype + ' * restrict ' + arg
 
         base_fields = OrderedDict()
         base_fields[ptr('E')] = self.E