diff --git a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device.rs b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device.rs
index 64ede77..1e3dfb2 100644
--- a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device.rs
+++ b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device.rs
@@ -251,6 +251,17 @@ impl DeviceStep {
             .memcpy_dtoh(&self.p_prime, &mut field.p_prime)
             .expect("p'");
         rt.stream.memcpy_dtoh(&self.sp, &mut field.sp).expect("sp");
+        // The previous step's field too (the control-volume route's
+        // unsteady term reads it).
+        rt.stream
+            .memcpy_dtoh(&self.u_old, &mut field.u_old)
+            .expect("u_old");
+        rt.stream
+            .memcpy_dtoh(&self.v_old, &mut field.v_old)
+            .expect("v_old");
+        rt.stream
+            .memcpy_dtoh(&self.w_old, &mut field.w_old)
+            .expect("w_old");
         rt.stream.synchronize().expect("sync");
     }