diff --git a/telephony/java/android/telephony/TelephonyManager.java b/telephony/java/android/telephony/TelephonyManager.java
index 58f1e8407d13a..7232ea7141800 100644
--- a/telephony/java/android/telephony/TelephonyManager.java
+++ b/telephony/java/android/telephony/TelephonyManager.java
@@ -2367,6 +2367,8 @@ public class TelephonyManager {
      *
      * @return the lowercase 2 character ISO-3166 country code, or empty string if not available.
      *
+     * @throws IllegalArgumentException when the slotIndex is invalid.
+     *
      * {@hide}
      */
     @SystemApi
@@ -2374,6 +2376,10 @@ public class TelephonyManager {
     @NonNull
     public String getNetworkCountryIso(int slotIndex) {
         try {
+            if (!SubscriptionManager.isValidSlotIndex(slotIndex)) {
+                throw new IllegalArgumentException("invalid slot index " + slotIndex);
+            }
+
             ITelephony telephony = getITelephony();
             if (telephony == null) return "";
             return telephony.getNetworkCountryIsoForPhone(slotIndex);