diff --git a/firedrake/assemble.py b/firedrake/assemble.py
index c55466086d..ba7b9d39a2 100644
--- a/firedrake/assemble.py
+++ b/firedrake/assemble.py
@@ -1745,7 +1745,7 @@ def _as_global_kernel_arg_output(_, self):
     if rank == 0:
         return op2.GlobalKernelArg((1,))
     elif rank == 1 or rank == 2 and self._diagonal:
-        V, = Vs
+        V = Vs[0]
         if V.ufl_element().family() == "Real":
             return op2.GlobalKernelArg((1,))
         else:
@@ -2052,7 +2052,7 @@ def _as_parloop_arg_output(_, self):
     if rank == 0:
         return op2.GlobalParloopArg(self._tensor)
     elif rank == 1 or rank == 2 and self._diagonal:
-        V, = Vs
+        V = Vs[0]
         if V.ufl_element().family() == "Real":
             return op2.GlobalParloopArg(self._tensor)
         else:
diff --git a/firedrake/slate/slate.py b/firedrake/slate/slate.py
index 942faf2bd8..f5af0d6cf3 100644
--- a/firedrake/slate/slate.py
+++ b/firedrake/slate/slate.py
@@ -1387,8 +1387,7 @@ def arg_function_spaces(self):
         """Returns a tuple of function spaces that the tensor
         is defined on.
         """
-        tensor, = self.operands
-        return tuple(arg.function_space() for arg in tensor.arguments())
+        return tuple(arg.function_space() for arg in self.arguments())
 
     def arguments(self):
         """Returns a tuple of arguments associated with the tensor."""
diff --git a/tests/firedrake/slate/test_linear_algebra.py b/tests/firedrake/slate/test_linear_algebra.py
index 23a2670217..d5c7dde997 100644
--- a/tests/firedrake/slate/test_linear_algebra.py
+++ b/tests/firedrake/slate/test_linear_algebra.py
@@ -152,10 +152,8 @@ def test_inverse_action(mat_type, rhs_type):
     assert np.allclose(x.dat.data, f.dat.data, rtol=1.e-13)
 
 
-@pytest.mark.parametrize("mat_type, rhs_type", [
-    ("slate", "slate"), ("slate", "form"), ("slate", "cofunction"),
-    ("aij", "cofunction"), ("aij", "form"),
-    ("matfree", "cofunction"), ("matfree", "form")])
+@pytest.mark.parametrize("rhs_type", ["slate", "form", "cofunction"])
+@pytest.mark.parametrize("mat_type", ["slate", "aij", "matfree"])
 def test_solve_interface(mat_type, rhs_type):
     mesh = UnitSquareMesh(1, 1)
     V = FunctionSpace(mesh, "HDivT", 0)
@@ -180,12 +178,8 @@ def test_solve_interface(mat_type, rhs_type):
     else:
         raise ValueError("Invalid rhs type")
 
-    sp = None
-    if mat_type == "matfree":
-        sp = {"pc_type": "none"}
-
     x = Function(V)
     problem = LinearVariationalProblem(A, b, x, bcs=bcs)
-    solver = LinearVariationalSolver(problem, solver_parameters=sp)
+    solver = LinearVariationalSolver(problem)
     solver.solve()
     assert np.allclose(x.dat.data, f.dat.data, rtol=1.e-13)