Index: kernel/arch/amd64/include/arch/cpu.h
===================================================================
--- kernel/arch/amd64/include/arch/cpu.h	(revision 811770c99b96760cdbd8d7f79f5e5bcb969a353e)
+++ kernel/arch/amd64/include/arch/cpu.h	(revision 57c2a87b03a0b6c08cef4f64f0cf52a7d8b38b62)
@@ -50,4 +50,5 @@
 #define RFLAGS_ID	(1 << 21)
 
+#define CR0_PE		(1 << 0)
 #define CR0_MP		(1 << 1)
 #define CR0_EM		(1 << 2)
Index: kernel/arch/amd64/src/smp/ap.S
===================================================================
--- kernel/arch/amd64/src/smp/ap.S	(revision 811770c99b96760cdbd8d7f79f5e5bcb969a353e)
+++ kernel/arch/amd64/src/smp/ap.S	(revision 57c2a87b03a0b6c08cef4f64f0cf52a7d8b38b62)
@@ -58,5 +58,5 @@
 	
 	movl %cr0, %eax
-	orl $1, %eax
+	orl $CR0_PE, %eax
 	movl %eax, %cr0     # switch to protected mode
 	jmpl $GDT_SELECTOR(KTEXT32_DES), $jump_to_kernel - BOOT_OFFSET + AP_BOOT_OFFSET