diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
index 4e44fd1f466ef122d53db3b1df34d04b651d6a31..d28128e0392c94c8bd0325fc4b9c4c239c0c81f6 100644
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -3625,16 +3625,21 @@ int __init probe_nr_irqs(void)
 {
 	int idx;
 	int nr = 0;
+#ifndef CONFIG_XEN
+	int nr_min = 32;
+#else
+	int nr_min = NR_IRQS;
+#endif
 
 	for (idx = 0; idx < nr_ioapics; idx++)
-		nr += io_apic_get_redir_entries(idx);
+		nr += io_apic_get_redir_entries(idx) + 1;
 
 	/* double it for hotplug and msi and nmi */
 	nr <<= 1;
 
 	/* something wrong ? */
-	if (nr < 32)
-		nr = 32;
+	if (nr < nr_min)
+		nr = nr_min;
 
 	return nr;
 }