Hello, The following MWE loops indefinitely for MPI_Comm_size in {2; 3}. Nothing fancy, just MatAIJ and MatDense. The problem is either in MatMPIDenseScatter() or MatMatMultSymbolic_MPIAIJ_MPIDense(), I believe, so if someone familiar with those routines can figure out a hot fix, I’m all ears. I could of course switch to a MatMult(), but the same infinite loop happens in another more complex code with A = rows=8, cols=35212 B = rows=35212, cols=9 So I’ll need a fix eventually. Thanks, Pierre