diff --git a/services/core/java/com/android/server/connectivity/Vpn.java b/services/core/java/com/android/server/connectivity/Vpn.java
index af4df1a..ea1924f 100644
--- a/services/core/java/com/android/server/connectivity/Vpn.java
+++ b/services/core/java/com/android/server/connectivity/Vpn.java
@@ -2023,6 +2023,13 @@
                     "usepeerdns", "idle", "1800", "mtu", "1400", "mru", "1400",
                     (profile.mppe ? "+mppe" : "nomppe"),
                 };
+                if (profile.mppe) {
+                    // Disallow PAP authentication when MPPE is requested, as MPPE cannot work
+                    // with PAP anyway, and users may not expect PAP (plain text) to be used when
+                    // MPPE was requested.
+                    mtpd = Arrays.copyOf(mtpd, mtpd.length + 1);
+                    mtpd[mtpd.length - 1] = "-pap";
+                }
                 break;
             case VpnProfile.TYPE_L2TP_IPSEC_PSK:
             case VpnProfile.TYPE_L2TP_IPSEC_RSA: