diff --git a/mm/mmap.c b/mm/mmap.c
index 2ba2743..e3c365f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -573,8 +573,12 @@
 	 */
 	if (vma->anon_vma && (importer || start != vma->vm_start)) {
 		anon_vma = vma->anon_vma;
+		VM_BUG_ON(adjust_next && next->anon_vma &&
+			  anon_vma != next->anon_vma);
+	} else if (adjust_next && next->anon_vma)
+		anon_vma = next->anon_vma;
+	if (anon_vma)
 		anon_vma_lock(anon_vma);
-	}
 
 	if (root) {
 		flush_dcache_mmap_lock(mapping);