diff --git a/firedrake/adjoint_utils/blocks/solving.py b/firedrake/adjoint_utils/blocks/solving.py
index 694f5de7a3..9eb6a8626c 100644
--- a/firedrake/adjoint_utils/blocks/solving.py
+++ b/firedrake/adjoint_utils/blocks/solving.py
@@ -80,8 +80,15 @@ def _init_solver_parameters(self, args, kwargs):
         self.assemble_kwargs = {}
 
     def __str__(self):
-        return "solve({} = {})".format(ufl2unicode(self.lhs),
-                                       ufl2unicode(self.rhs))
+        try:
+            lhs_string = ufl2unicode(self.lhs)
+        except AttributeError:
+            lhs_string = str(self.lhs)
+        try:
+            rhs_string = ufl2unicode(self.rhs)
+        except AttributeError:
+            rhs_string = str(self.rhs)
+        return "solve({} = {})".format(lhs_string, rhs_string)
 
     def _create_F_form(self):
         # Process the equation forms, replacing values with checkpoints,