diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index c0dd35f1af12..e4882b73120e 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -1238,6 +1238,10 @@ astute users may notice some differences in behavior:
 
 - DAX (Direct Access) is not supported on encrypted files.
 
+- Encrypted files cannot be used directly as swap files.  To swap to
+  an encrypted file, set up a loopback device on top of it.
+  Alternatively, encrypted swap can use a dm-crypt device.
+
 - The maximum length of an encrypted symlink is 2 bytes shorter than
   the maximum length of an unencrypted symlink.  For example, on an
   EXT4 filesystem with a 4K block size, unencrypted symlinks can be up
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4e07d457e261..d7f749ad60c2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3668,6 +3668,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		error = -EBUSY;
 		goto bad_swap_unlock_inode;
 	}
+	if (IS_ENCRYPTED(inode)) {
+		pr_warn_once(
+			"Filesystem-level encrypted swapfile '%s' is unsupported. Create a loop device over it, or use dm-crypt\n",
+			name->name);
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
 
 	/*
 	 * The swap subsystem needs a major overhaul to support this.