diff --git a/exercise3/wave_1d_parallel.c b/exercise3/wave_1d_parallel.c
index ef9847c..e9e4d86 100644
--- a/exercise3/wave_1d_parallel.c
+++ b/exercise3/wave_1d_parallel.c
@@ -96,7 +96,7 @@ void move_buffer_window(void) {
 // Derive step t+1 from steps t and t-1.
 void time_step(void) {
   // BEGIN: T4
-  for (int_t i = 0; i < N; i++) {
+  for (int_t i = 0; i < n; i++) {
     U_nxt(i) = -U_prv(i) + 2.0 * U(i) + (dt * dt * c * c) / (dx * dx) * (U(i - 1) + U(i + 1) - 2.0 * U(i));
   }
   // END: T4