diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index 0fc227803a..509343e0be 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -217,6 +217,7 @@ MemMapInitialization (
     UINT32  PciSize;
 
     TopOfLowRam = GetSystemMemorySizeBelow4gb ();
+    PciExBarBase = 0;
     if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
       //
       // The MMCONFIG area is expected to fall between the top of low RAM and