diff --git a/gusto/time_discretisation/explicit_runge_kutta.py b/gusto/time_discretisation/explicit_runge_kutta.py
index c1113db5b..6bfaa5d57 100644
--- a/gusto/time_discretisation/explicit_runge_kutta.py
+++ b/gusto/time_discretisation/explicit_runge_kutta.py
@@ -230,9 +230,7 @@ def solve_stage(self, x0, stage):
                 self.limiter.apply(self.x1)
 
             # Set initial guess for solver
-            if (stage == 0):
-                self.x_out.assign(x0)
-            else:
+            if (stage > 0):
                 self.x_out.assign(self.k[stage-1])
             self.solver.solve()
 
diff --git a/gusto/time_discretisation/implicit_runge_kutta.py b/gusto/time_discretisation/implicit_runge_kutta.py
index a40acff92..e973e0b22 100644
--- a/gusto/time_discretisation/implicit_runge_kutta.py
+++ b/gusto/time_discretisation/implicit_runge_kutta.py
@@ -141,9 +141,7 @@ def solve_stage(self, x0, stage):
             self.xnph = self.x1 + self.butcher_matrix[stage, stage]*self.dt*self.x_out
         solver = self.solvers[stage]
         # Set initial guess for solver
-        if (stage == 0):
-            self.x_out.assign(x0)
-        else:
+        if (stage > 0):
             self.x_out.assign(self.k[stage-1])
 
         solver.solve()