diff --git a/src/palace_tools/models/api/rwpm_audiobook.py b/src/palace_tools/models/api/rwpm_audiobook.py
index c21045c..6f64875 100644
--- a/src/palace_tools/models/api/rwpm_audiobook.py
+++ b/src/palace_tools/models/api/rwpm_audiobook.py
@@ -45,12 +45,23 @@ def from_track(cls, track: AudioTrack, default_title: str = "Track") -> Self:
 ToCEntries = Sequence[ToCEntry]
 
 
+class AudioTrackEncryption(BaseModel):
+    scheme: str
+    algorithm: str
+    profile: str
+
+
+class AudioTrackProperties(BaseModel):
+    encrypted: AudioTrackEncryption | None = None
+
+
 class AudioTrack(BaseModel):
     title: str | None = None
     href: str
     content_type: str = Field(..., alias="type")
     duration: int  # in seconds
     bitrate: int | None = None
+    properties: AudioTrackProperties | None = None
 
     # Optional property, initialized after the model is created, if
     # we have the source file, this is the actual duration as read from the