diff --git a/arch/x86/lib/physmem.c b/arch/x86/lib/physmem.c
index 18f0e62..59b3fe9 100644
--- a/arch/x86/lib/physmem.c
+++ b/arch/x86/lib/physmem.c
@@ -12,6 +12,8 @@
 #include <physmem.h>
 #include <linux/compiler.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 /* Large pages are 2MB. */
 #define LARGE_PAGE_SIZE ((1 << 20) * 2)