diff --git a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/model/mapper/ModelMapper.kt b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/model/mapper/ModelMapper.kt
index 179fa7dd..1c2c70ea 100644
--- a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/model/mapper/ModelMapper.kt
+++ b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/model/mapper/ModelMapper.kt
@@ -184,7 +184,7 @@ open class ModelMapper(
         val methodName = parameters.methodName
 
         // we filter out iTAN and Einschritt-Verfahren as they are not permitted anymore according to PSD2
-        if (methodName.toLowerCase() == "itan") {
+        if (methodName.lowercase() == "itan") {
             return null
         }
 
@@ -196,7 +196,7 @@ open class ModelMapper(
     }
 
     protected open fun mapToTanMethodType(parameters: TanMethodParameters): TanMethodType? {
-        val name = parameters.methodName.toLowerCase()
+        val name = parameters.methodName.lowercase()
 
         return when {
             // names are like 'chipTAN (comfort) manuell', 'Smart(-)TAN plus (manuell)' and
@@ -254,7 +254,7 @@ open class ModelMapper(
 
     protected open fun tanMethodNameContains(name: String, vararg namesToTest: String): Boolean {
         namesToTest.forEach { nameToTest ->
-            if (name.contains(nameToTest.toLowerCase())) {
+            if (name.contains(nameToTest.lowercase())) {
                 return true
             }
         }
diff --git a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/BankResponse.kt b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/BankResponse.kt
index 52843345..65de8646 100644
--- a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/BankResponse.kt
+++ b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/BankResponse.kt
@@ -1,3 +1,5 @@
+@file:Suppress("UNCHECKED_CAST")
+
 package net.codinux.banking.fints.response
 
 import net.codinux.banking.fints.messages.MessageBuilderResult
diff --git a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/ResponseParser.kt b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/ResponseParser.kt
index d3011ef5..8ef27dfc 100644
--- a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/ResponseParser.kt
+++ b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/response/ResponseParser.kt
@@ -498,7 +498,7 @@ open class ResponseParser(
         }
 
         try {
-            val lowerCaseMayDkTanMethod = mayDkTanMethod.toLowerCase()
+            val lowerCaseMayDkTanMethod = mayDkTanMethod.lowercase()
 
             if (lowerCaseMayDkTanMethod == "mobiletan" || lowerCaseMayDkTanMethod == "mtan") {
                 return DkTanMethod.mobileTAN
diff --git a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/tan/FlickerCodeDecoder.kt b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/tan/FlickerCodeDecoder.kt
index 9abfa5ae..b5db757f 100644
--- a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/tan/FlickerCodeDecoder.kt
+++ b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/tan/FlickerCodeDecoder.kt
@@ -84,7 +84,7 @@ open class FlickerCodeDecoder {
         }
 
         if (encoding == FlickerCodeEncoding.ASCII) {
-            data = data.map { toHex(it.toInt(), 2) }.joinToString("")
+            data = data.map { toHex(it.code, 2) }.joinToString("")
         }
 
         if (encoding == FlickerCodeEncoding.BCD && data.length % 2 != 0) {
@@ -193,7 +193,7 @@ open class FlickerCodeDecoder {
 
 
     protected open fun toHex(number: Int, minLength: Int): String {
-        var result = number.toString (16).toUpperCase()
+        var result = number.toString (16).uppercase()
 
         while (result.length < minLength) {
             result = '0' + result
diff --git a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/util/Base64.kt b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/util/Base64.kt
index c04d046f..2bc77146 100644
--- a/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/util/Base64.kt
+++ b/fints4k/src/commonMain/kotlin/net/codinux/banking/fints/util/Base64.kt
@@ -37,9 +37,9 @@ open class Base64 {
 
         (string.indices step 3).forEach { index ->
             val number: Int =
-                (0xFF.and(string[index    ].toInt()) shl 16) +
-                (0xFF.and(string[index + 1].toInt()) shl  8) +
-                 0xFF.and(string[index + 2].toInt())
+                (0xFF.and(string[index    ].code) shl 16) +
+                (0xFF.and(string[index + 1].code) shl  8) +
+                 0xFF.and(string[index + 2].code)
 
             encoded.append(Base64Chars[(number shr 18) and 0x3F])
             encoded.append(Base64Chars[(number shr 12) and 0x3F])