diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index 21b95b342c71446c4c04ccf45e14ea91055407a3..6deeb19e3f08492b2bf32e0aa3b6c122c43a3ada 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -501,6 +501,12 @@ static void spapr_phb_realize(DeviceState *dev, Error **errp)
             return;
         }
 
+        if (sphb->index > SPAPR_PCI_MAX_INDEX) {
+            error_setg(errp, "\"index\" for PAPR PHB is too large (max %u)",
+                       SPAPR_PCI_MAX_INDEX);
+            return;
+        }
+
         sphb->buid = SPAPR_PCI_BASE_BUID + sphb->index;
         sphb->dma_liobn = SPAPR_PCI_BASE_LIOBN + sphb->index;
 
@@ -669,7 +675,7 @@ static void spapr_phb_reset(DeviceState *qdev)
 }
 
 static Property spapr_phb_properties[] = {
-    DEFINE_PROP_INT32("index", sPAPRPHBState, index, -1),
+    DEFINE_PROP_UINT32("index", sPAPRPHBState, index, -1),
     DEFINE_PROP_UINT64("buid", sPAPRPHBState, buid, -1),
     DEFINE_PROP_UINT32("liobn", sPAPRPHBState, dma_liobn, -1),
     DEFINE_PROP_UINT64("mem_win_addr", sPAPRPHBState, mem_win_addr, -1),
diff --git a/include/hw/pci-host/spapr.h b/include/hw/pci-host/spapr.h
index 4ea2a0d14aa717cc2f2af0301444a9c7367a585c..876ecf09eaef4a096df32e61027bb76b9f190772 100644
--- a/include/hw/pci-host/spapr.h
+++ b/include/hw/pci-host/spapr.h
@@ -64,7 +64,7 @@ typedef struct spapr_pci_msi_mig {
 struct sPAPRPHBState {
     PCIHostState parent_obj;
 
-    int32_t index;
+    uint32_t index;
     uint64_t buid;
     char *dtbusname;
 
@@ -94,6 +94,8 @@ struct sPAPRPHBVFIOState {
     int32_t iommugroupid;
 };
 
+#define SPAPR_PCI_MAX_INDEX          255
+
 #define SPAPR_PCI_BASE_BUID          0x800000020000000ULL
 
 #define SPAPR_PCI_WINDOW_BASE        0x10000000000ULL