diff --git a/mm/internal.h b/mm/internal.h
index 858ad01..1f43f74 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -16,6 +16,8 @@
 void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
 		unsigned long floor, unsigned long ceiling);
 
+extern void prep_compound_page(struct page *page, unsigned long order);
+
 static inline void set_page_count(struct page *page, int v)
 {
 	atomic_set(&page->_count, v);