diff --git a/src/commonMain/kotlin/com/infendro/kdf/PBKDF2.kt b/src/commonMain/kotlin/com/infendro/kdf/PBKDF2.kt
index 6cd38f6..8c83875 100644
--- a/src/commonMain/kotlin/com/infendro/kdf/PBKDF2.kt
+++ b/src/commonMain/kotlin/com/infendro/kdf/PBKDF2.kt
@@ -7,7 +7,7 @@ import com.infendro.hash.HashFunction
 import com.infendro.mac.HMAC
 
 class PBKDF2(
-    function: HashFunction,
+    private val function: HashFunction,
 ) {
     private val hmac = HMAC(function)
 
@@ -18,7 +18,7 @@ class PBKDF2(
         length: Int,
     ): ByteArray {
         val key = buildList {
-            for (i in 1..(length + size - 1) / size) {
+            for (i in 1..(length + function.bytes - 1) / function.bytes) {
                 val input = salt + i.toUInt().toByteArray()
 
                 var u = hmac.hash(value, input)