diff --git a/app-common/src/main/java/im/angry/openeuicc/ui/wizard/DownloadWizardDetailsFragment.kt b/app-common/src/main/java/im/angry/openeuicc/ui/wizard/DownloadWizardDetailsFragment.kt
index 69ed77f..88567c2 100644
--- a/app-common/src/main/java/im/angry/openeuicc/ui/wizard/DownloadWizardDetailsFragment.kt
+++ b/app-common/src/main/java/im/angry/openeuicc/ui/wizard/DownloadWizardDetailsFragment.kt
@@ -87,13 +87,7 @@ private fun isValidIMEI(input: CharSequence): Boolean {
 
     fun sumOfDigits(input: Int): Int {
         if (input % 2 == 0) return input
-        var n = input
-        var sum = 0
-        while (n > 0) {
-            sum += n % 10
-            n /= 10
-        }
-        return sum
+        return (input * 2).toString().map(Char::digitToInt).sum()
     }
 
     val sum = input.dropLast(1).map(Char::digitToInt).sumOf(::sumOfDigits)