diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ef51ed87ef383ea2eaf0e7de41d49c5b76c245b9..4b20f0fd949ea81200fa3144f06d6b7d0260231e 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -406,8 +406,12 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 
 	BUG_ON(ctx->mm != mm);
 
+#ifdef CONFIG_USERSWAP
+	VM_BUG_ON(uswap_vm_flag_bug_on(reason));
+#else
 	VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
 	VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
+#endif
 
 	if (ctx->features & UFFD_FEATURE_SIGBUS)
 		goto out;
diff --git a/include/linux/userswap.h b/include/linux/userswap.h
index 82cc79584e4362078dda37ac7a586f0c41e6a99f..6c96cef2ec9bcc4ee4ddf206e9617434bc154c08 100644
--- a/include/linux/userswap.h
+++ b/include/linux/userswap.h
@@ -47,6 +47,18 @@ static inline bool uswap_validate_mremap_flags(unsigned long flags)
 	return true;
 }
 
+/* When CONFIG_USERSWAP=y, VM_UFFD_MISSING|VM_USWAP is right;
+ * 0 or > 1 flags set is a bug; we expect exactly 1.
+ */
+static inline bool uswap_vm_flag_bug_on(unsigned long reason)
+{
+	if (reason & ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_USWAP))
+		return true;
+	if (reason & VM_USWAP)
+		return !(reason & VM_UFFD_MISSING) || reason & ~(VM_USWAP|VM_UFFD_MISSING);
+	return !(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP);
+}
+
 #endif /* CONFIG_USERSWAP */
 
 #endif /* _LINUX_USERSWAP_H */