diff --git a/services/tunnelbroker/src/websockets/session.rs b/services/tunnelbroker/src/websockets/session.rs
--- a/services/tunnelbroker/src/websockets/session.rs
+++ b/services/tunnelbroker/src/websockets/session.rs
@@ -21,10 +21,12 @@
 use notifs::fcm::error::Error::FCMError as NotifsFCMError;
 use notifs::web_push::error::Error::WebPush as NotifsWebPushError;
 use notifs::wns::error::Error::WNSNotification as NotifsWNSError;
+use reqwest::Url;
 use tokio::io::AsyncRead;
 use tokio::io::AsyncWrite;
 use tracing::{debug, error, info, trace};
 use tunnelbroker_messages::bad_device_token::BadDeviceToken;
+use tunnelbroker_messages::Platform;
 use tunnelbroker_messages::{
   message_to_device_request_status::Failure,
   message_to_device_request_status::MessageSentStatus, session::DeviceTypes,
@@ -304,6 +306,33 @@
       MessageToTunnelbroker::SetDeviceTokenWithPlatform(
         token_with_platform,
       ) => {
+        if matches!(token_with_platform.platform, Platform::Windows) {
+          let Ok(parsed_url) = Url::parse(&token_with_platform.device_token)
+          else {
+            debug!(
+              device_token = &token_with_platform.device_token,
+              device_id = &self.device_info.device_id,
+              "Device token could not be parsed as a URL"
+            );
+            return Err(SessionError::InvalidDeviceToken);
+          };
+          let Some(domain) = parsed_url.domain() else {
+            debug!(
+              device_token = &token_with_platform.device_token,
+              device_id = &self.device_info.device_id,
+              "Domain missing from device token URL"
+            );
+            return Err(SessionError::InvalidDeviceToken);
+          };
+          if !domain.ends_with("notify.windows.com") {
+            debug!(
+              device_token = &token_with_platform.device_token,
+              device_id = &self.device_info.device_id,
+              "Device token URL contains invalid domain"
+            );
+            return Err(SessionError::InvalidDeviceToken);
+          }
+        }
         self
           .db_client
           .set_device_token(