the offset in the part array should be a size_t.

src/engine.c

@@ -604,7 +604,7 @@ void engine_exchange_cells(struct engine *e) {
  * @return The number of arrived parts copied to parts and xparts.
  */
 
-int engine_exchange_strays(struct engine *e, int offset, int *ind, size_t N) {
+int engine_exchange_strays(struct engine *e, size_t offset, int *ind, size_t N) {
 
 #ifdef WITH_MPI
 

src/engine.h

@@ -182,7 +182,7 @@ void engine_init_particles(struct engine *e);
 void engine_step(struct engine *e);
 void engine_maketasks(struct engine *e);
 void engine_split(struct engine *e, struct partition *initial_partition);
-int engine_exchange_strays(struct engine *e, int offset, int *ind, size_t N);
+int engine_exchange_strays(struct engine *e, size_t offset, int *ind, size_t N);
 void engine_rebuild(struct engine *e);
 void engine_repartition(struct engine *e);
 void engine_makeproxies(struct engine *e);