diff --git a/src/parallel_io.c b/src/parallel_io.c
index 8bd7a41d663fff89eee0266f14af24ebfaea9837..b62422d22fb099e0b4da31a0bd1063b952268575 100644
--- a/src/parallel_io.c
+++ b/src/parallel_io.c
@@ -994,8 +994,8 @@ void prepare_file(struct engine* e, const char* baseName, long long N_total[6],
       units_conversion_factor(internal_units, snapshot_units, UNIT_CONV_LENGTH);
   const double dblTime = e->time * factor_time;
   const double dim[3] = {e->s->dim[0] * factor_length,
-                         e->s->dim[0] * factor_length,
-                         e->s->dim[0] * factor_length};
+                         e->s->dim[1] * factor_length,
+                         e->s->dim[2] * factor_length};
 
   /* Print the relevant information and print status */
   io_write_attribute(h_grp, "BoxSize", DOUBLE, dim, 3);
diff --git a/src/serial_io.c b/src/serial_io.c
index 5b155057883b6b0e3131c3732b9f3120d17df8a4..c05c43a6521d46f5145d5bc29ad544c82e39ff04 100644
--- a/src/serial_io.c
+++ b/src/serial_io.c
@@ -856,8 +856,8 @@ void write_output_serial(struct engine* e, const char* baseName,
         internal_units, snapshot_units, UNIT_CONV_LENGTH);
     const double dblTime = e->time * factor_time;
     const double dim[3] = {e->s->dim[0] * factor_length,
-                           e->s->dim[0] * factor_length,
-                           e->s->dim[0] * factor_length};
+                           e->s->dim[1] * factor_length,
+                           e->s->dim[2] * factor_length};
 
     /* Print the relevant information and print status */
     io_write_attribute(h_grp, "BoxSize", DOUBLE, dim, 3);
diff --git a/src/single_io.c b/src/single_io.c
index f908c4581cb57d535548f1419633bb8ff8c8a164..178f59a528016ddf6e642ac4e81deda72f508f85 100644
--- a/src/single_io.c
+++ b/src/single_io.c
@@ -709,8 +709,8 @@ void write_output_single(struct engine* e, const char* baseName,
       units_conversion_factor(internal_units, snapshot_units, UNIT_CONV_LENGTH);
   const double dblTime = e->time * factor_time;
   const double dim[3] = {e->s->dim[0] * factor_length,
-                         e->s->dim[0] * factor_length,
-                         e->s->dim[0] * factor_length};
+                         e->s->dim[1] * factor_length,
+                         e->s->dim[2] * factor_length};
 
   /* Print the relevant information and print status */
   io_write_attribute(h_grp, "BoxSize", DOUBLE, dim, 3);