diff --git a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
index ff837035ca..65d0ef9252 100644
--- a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
+++ b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
@@ -221,6 +221,10 @@ PciHostBridgeGetRootBridges (
     return ScanForRootBridges (Count);
   }
 
+  ZeroMem (&Io, sizeof (Io));
+  ZeroMem (&Mem, sizeof (Mem));
+  ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
+
   Attributes = EFI_PCI_ATTRIBUTE_IDE_PRIMARY_IO |
     EFI_PCI_ATTRIBUTE_IDE_SECONDARY_IO |
     EFI_PCI_ATTRIBUTE_ISA_IO_16 |
diff --git a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
index 31c63ae19e..920417950a 100644
--- a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
+++ b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
@@ -202,8 +202,13 @@ ScanForRootBridges (
   for (PrimaryBus = 0; PrimaryBus <= PCI_MAX_BUS; PrimaryBus = SubBus + 1) {
     SubBus = PrimaryBus;
     Attributes = 0;
+
+    ZeroMem (&Io, sizeof (Io));
+    ZeroMem (&Mem, sizeof (Mem));
+    ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
+    ZeroMem (&PMem, sizeof (PMem));
+    ZeroMem (&PMemAbove4G, sizeof (PMemAbove4G));
     Io.Base = Mem.Base = MemAbove4G.Base = PMem.Base = PMemAbove4G.Base = MAX_UINT64;
-    Io.Limit = Mem.Limit = MemAbove4G.Limit = PMem.Limit = PMemAbove4G.Limit = 0;
     //
     // Scan all the PCI devices on the primary bus of the PCI root bridge
     //