diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index d1c92cf77f..7e5f4b8a00 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -585,8 +585,8 @@ static void cf_check bar_write(
         /* If the value written is the current one avoid printing a warning. */
         if ( val != (uint32_t)(bar->addr >> (hi ? 32 : 0)) )
             gprintk(XENLOG_WARNING,
-                    "%pp: ignored BAR %zu write while mapped\n",
-                    &pdev->sbdf, bar - pdev->vpci->header.bars + hi);
+                    "%pp: ignored BAR %u write while mapped\n",
+                    &pdev->sbdf, (reg - PCI_BASE_ADDRESS_0) / 4);
         return;
     }
 
@@ -646,8 +646,8 @@ static void cf_check guest_mem_bar_write(const struct pci_dev *pdev,
         /* If the value written is the current one avoid printing a warning. */
         if ( guest_addr != bar->guest_addr )
             gprintk(XENLOG_WARNING,
-                    "%pp: ignored guest BAR %zu write while mapped\n",
-                    &pdev->sbdf, bar - pdev->vpci->header.bars + hi);
+                    "%pp: ignored guest BAR %u write while mapped\n",
+                    &pdev->sbdf, (reg - PCI_BASE_ADDRESS_0) / 4);
         return;
     }
     bar->guest_addr = guest_addr;