diff --git a/arch/x86/include/asm/microcode.h b/arch/x86/include/asm/microcode.h
index 0478935..29bf060 100644
--- a/arch/x86/include/asm/microcode.h
+++ b/arch/x86/include/asm/microcode.h
@@ -9,6 +9,9 @@
 
 #ifndef __ASSEMBLY__
 
+/* This is a declaration for ucode_base in start.S */
+extern u32 ucode_base;
+
 /**
  * microcode_update_intel() - Apply microcode updates
  *