diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 01e2de4d254026ff8089533aae9d46b6c6b372a3..ad3b7fc24a0500360f8f4e10db19f8194775ee36 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -614,6 +614,7 @@ void __init setup_arch(char **cmdline_p)
 	 * we are rounding upwards:
 	 */
 	end_pfn = e820_end_of_ram();
+	num_physpages = end_pfn;		/* for pfn_valid */
 
 	check_efer();