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 5fa8002..69ed77f 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
@@ -48,9 +48,8 @@ class DownloadWizardDetailsFragment : DownloadWizardActivity.DownloadWizardStepF
         matchingId = view.requireViewById(R.id.profile_download_code)
         confirmationCode = view.requireViewById(R.id.profile_download_confirmation_code)
         imei = view.requireViewById(R.id.profile_download_imei)
-        smdp.editText!!.addTextChangedListener {
-            updateInputCompleteness()
-        }
+        smdp.editText!!.addTextChangedListener { updateInputCompleteness() }
+        imei.editText!!.addTextChangedListener { updateInputCompleteness() }
         return view
     }
 
@@ -69,7 +68,34 @@ class DownloadWizardDetailsFragment : DownloadWizardActivity.DownloadWizardStepF
     }
 
     private fun updateInputCompleteness() {
-        inputComplete = Patterns.DOMAIN_NAME.matcher(smdp.editText!!.text).matches()
+        inputComplete = runCatching(::validate).isSuccess
         refreshButtons()
     }
-}
\ No newline at end of file
+
+    private fun validate() {
+        check(Patterns.DOMAIN_NAME.matcher(smdp.editText!!.text).matches()) {
+            "Invalid SM-DP+ address"
+        }
+        check(imei.editText!!.text.let { it.isEmpty() || isValidIMEI(it) }) {
+            "Invalid IMEI"
+        }
+    }
+}
+
+private fun isValidIMEI(input: CharSequence): Boolean {
+    if (input.length != 15 || !input.all(Char::isDigit)) return false
+
+    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
+    }
+
+    val sum = input.dropLast(1).map(Char::digitToInt).sumOf(::sumOfDigits)
+    return (sum * 9) % 10 == input.last().digitToInt()
+}