diff --git a/sumpy/tools.py b/sumpy/tools.py
index c826ef2fe8ea4d3f96e3b8b816dd3500f5efaae8..863b4bb91749adef6ea65a374d697ecfa8d30bc4 100644
--- a/sumpy/tools.py
+++ b/sumpy/tools.py
@@ -299,7 +299,7 @@ class KernelComputation(object):
                 lp.Assignment(id=None,
                     assignee="knl_%d_scaling" % i,
                     expression=sympy_conv(kernel.get_global_scaling_const()),
-                    temp_var_type=dtype)
+                    temp_var_type=lp.Optional(dtype))
                 for i, (kernel, dtype) in enumerate(
                     zip(self.kernels, self.value_dtypes))]