diff --git a/mm/mmap.c b/mm/mmap.c
index 3eda23c9ebe7..3937479d0e07 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -615,6 +615,7 @@ static inline int dup_anon_vma(struct vm_area_struct *dst,
 	 * anon pages imported.
 	 */
 	if (src->anon_vma && !dst->anon_vma) {
+		vma_start_write(dst);
 		dst->anon_vma = src->anon_vma;
 		return anon_vma_clone(dst, src);
 	}