diff --git a/src/arch/x86_64/boot.asm b/src/arch/x86_64/boot.asm
index 3e8e594..98155c2 100644
--- a/src/arch/x86_64/boot.asm
+++ b/src/arch/x86_64/boot.asm
@@ -12,6 +12,9 @@ start:
     call set_up_page_tables
     call enable_paging
 
+    ; load the 64-bit GDT
+    lgdt [gdt64.pointer]
+
     ; print `OK` to screen
     mov dword [0xb8000], 0x2f4b2f4f
     hlt
@@ -147,3 +150,11 @@ p2_table:
 stack_bottom:
     resb 64
 stack_top:
+
+section .rodata
+gdt64:
+    dq 0 ; zero entry
+    dq (1<<43) | (1<<44) | (1<<47) | (1<<53) ; code segment
+.pointer:
+    dw $ - gdt64 - 1
+    dq gdt64