diff --git a/tests/firedrake/regression/test_interp_dual.py b/tests/firedrake/regression/test_interp_dual.py
index 73428e0cc6..21c73c804c 100644
--- a/tests/firedrake/regression/test_interp_dual.py
+++ b/tests/firedrake/regression/test_interp_dual.py
@@ -43,6 +43,7 @@ def test_interp_self(V1):
 
 def test_assemble_interp_adjoint_tensor(mesh, V1, f1):
     a = assemble(TestFunction(V1) * dx)
+    # We want tensor to be a dependency of the input expression for this test
     assemble(action(adjoint(Interpolate(f1 * TestFunction(V1), V1)), a),
              tensor=a)