diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index bbec618a614b..f84f167ec04c 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -50,7 +50,7 @@ static inline void page_ext_init(void)
 }
 #endif
 
-struct page_ext *lookup_page_ext(struct page *page);
+struct page_ext *lookup_page_ext(const struct page *page);
 
 #else /* !CONFIG_PAGE_EXTENSION */
 struct page_ext;
@@ -59,7 +59,7 @@ static inline void pgdat_page_ext_init(struct pglist_data *pgdat)
 {
 }
 
-static inline struct page_ext *lookup_page_ext(struct page *page)
+static inline struct page_ext *lookup_page_ext(const struct page *page)
 {
 	return NULL;
 }
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 5295ef331165..a9826da84ccb 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -120,7 +120,7 @@ void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
 	pgdat->node_page_ext = NULL;
 }
 
-struct page_ext *lookup_page_ext(struct page *page)
+struct page_ext *lookup_page_ext(const struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	unsigned long index;
@@ -195,7 +195,7 @@ fail:
 
 #else /* CONFIG_FLAT_NODE_MEM_MAP */
 
-struct page_ext *lookup_page_ext(struct page *page)
+struct page_ext *lookup_page_ext(const struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	struct mem_section *section = __pfn_to_section(pfn);