diff --git a/telephony/java/android/telephony/TelephonyManager.java b/telephony/java/android/telephony/TelephonyManager.java
index f29a6ed083998..0c8d669804a4f 100644
--- a/telephony/java/android/telephony/TelephonyManager.java
+++ b/telephony/java/android/telephony/TelephonyManager.java
@@ -2291,7 +2291,8 @@ public class TelephonyManager {
     }
 
     /**
-     * Returns the voice mail count. Return 0 if unavailable.
+     * Returns the voice mail count. Return 0 if unavailable, -1 if there are unread voice messages
+     * but the count is unknown,
      * <p>
      * Requires Permission:
      *   {@link android.Manifest.permission#READ_PHONE_STATE READ_PHONE_STATE}