diff --git a/internal/subsonic/errors.go b/internal/subsonic/errors.go
new file mode 100644
index 00000000..a7028510
--- /dev/null
+++ b/internal/subsonic/errors.go
@@ -0,0 +1,17 @@
+package subsonic
+
+// Subsonic REST error codes per http://www.subsonic.org/pages/api.jsp §3.
+// ErrTokenNotSupported (41) is reused for "this user has not enabled the
+// requested auth mode" — the historical meaning ("LDAP users can't use
+// token auth") is the closest analogue.
+const (
+	ErrGeneric           = 0
+	ErrMissingParameter  = 10
+	ErrClientTooOld      = 20
+	ErrServerTooOld      = 30
+	ErrWrongCredentials  = 40
+	ErrTokenNotSupported = 41
+	ErrNotAuthorized     = 50
+	ErrTrialExpired      = 60
+	ErrDataNotFound      = 70
+)