diff --git a/firedrake/slate/slac/compiler.py b/firedrake/slate/slac/compiler.py
index 46611aaf01..7dedd21e10 100644
--- a/firedrake/slate/slac/compiler.py
+++ b/firedrake/slate/slac/compiler.py
@@ -67,12 +67,6 @@
 cell_to_facets_dtype = np.dtype(np.int8)
 
 
-def _cache_key(expr, compiler_parameters):
-    return expr.ufl_domains()[0].comm, md5(
-        (expr.expression_hash + str(sorted(compiler_parameters.items()))).encode()
-    ).hexdigest()
-
-
 class SlateKernel(TSFCKernel):
     def __init__(self, expr, compiler_parameters):
         self.split_kernel = generate_loopy_kernel(expr, compiler_parameters)
diff --git a/firedrake/tsfc_interface.py b/firedrake/tsfc_interface.py
index 245663d8c1..a4a57ae0cb 100644
--- a/firedrake/tsfc_interface.py
+++ b/firedrake/tsfc_interface.py
@@ -55,8 +55,6 @@
 
 def tsfc_compile_form_hashkey(form, prefix, parameters, interface, diagonal, log):
     # Drop prefix as it's only used for naming and log
-    # JBTODO: Can't drop prefix as tests/slate/test_optimise.py::test_partially_optimised fails, investigate
-    # it looks like the prefix is being used to create different subkernels, which conflicts with the docstring below
     return default_parallel_hashkey(form.signature(), prefix, parameters, interface, diagonal)