diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 963a41c7f5..2d2f4a7c41 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -695,10 +695,15 @@ static const MemoryRegionOps s390_msi_ctrl_ops = {
 
 void s390_pci_iommu_enable(S390PCIIOMMU *iommu)
 {
+    /*
+     * The iommu region is initialized against a 0-mapped address space,
+     * so the smallest IOMMU region we can define runs from 0 to the end
+     * of the PCI address space.
+     */
     char *name = g_strdup_printf("iommu-s390-%04x", iommu->pbdev->uid);
     memory_region_init_iommu(&iommu->iommu_mr, sizeof(iommu->iommu_mr),
                              TYPE_S390_IOMMU_MEMORY_REGION, OBJECT(&iommu->mr),
-                             name, iommu->pal - iommu->pba + 1);
+                             name, iommu->pal + 1);
     iommu->enabled = true;
     memory_region_add_subregion(&iommu->mr, 0, MEMORY_REGION(&iommu->iommu_mr));
     g_free(name);