diff --git a/OvmfPkg/XenBusDxe/XenStore.c b/OvmfPkg/XenBusDxe/XenStore.c
index 76b6e297ef..6812e1078c 100644
--- a/OvmfPkg/XenBusDxe/XenStore.c
+++ b/OvmfPkg/XenBusDxe/XenStore.c
@@ -1304,6 +1304,7 @@ XenStoreTransactionEnd (
 }
 
 XENSTORE_STATUS
+EFIAPI
 XenStoreVSPrint (
   IN CONST XENSTORE_TRANSACTION *Transaction,
   IN CONST CHAR8           *DirectoryPath,
diff --git a/OvmfPkg/XenBusDxe/XenStore.h b/OvmfPkg/XenBusDxe/XenStore.h
index c9d4c6509a..33bb647f66 100644
--- a/OvmfPkg/XenBusDxe/XenStore.h
+++ b/OvmfPkg/XenBusDxe/XenStore.h
@@ -209,6 +209,7 @@ XenStoreSPrint (
            indicating the type of write failure.
 **/
 XENSTORE_STATUS
+EFIAPI
 XenStoreVSPrint (
   IN CONST XENSTORE_TRANSACTION *Transaction,
   IN CONST CHAR8           *DirectoryPath,