diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
index 072a04e318..894e131c00 100644
--- a/hw/pci-host/piix.c
+++ b/hw/pci-host/piix.c
@@ -140,7 +140,7 @@ static void i440fx_update_memory_mappings(PCII440FXState *d)
     memory_region_transaction_begin();
     for (i = 0; i < 13; i++) {
         pam_update(&d->pam_regions[i], i,
-                   pd->config[I440FX_PAM + ((i + 1) / 2)]);
+                   pd->config[I440FX_PAM + (DIV_ROUND_UP(i, 2))]);
     }
     memory_region_set_enabled(&d->smram_region,
                               !(pd->config[I440FX_SMRAM] & SMRAM_D_OPEN));