diff --git a/mm/mprotect.c b/mm/mprotect.c
index 063bbed..ec91dfd 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -304,6 +304,7 @@
 			   vma->vm_userfaultfd_ctx);
 	if (*pprev) {
 		vma = *pprev;
+		VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
 		goto success;
 	}