diff --git a/src/test/kotlin/de/gmuth/ipp/core/IppOperationsTests.kt b/src/test/kotlin/de/gmuth/ipp/core/IppOperationsTests.kt
index e316c03b..29b75a0b 100644
--- a/src/test/kotlin/de/gmuth/ipp/core/IppOperationsTests.kt
+++ b/src/test/kotlin/de/gmuth/ipp/core/IppOperationsTests.kt
@@ -1,19 +1,19 @@
 package de.gmuth.ipp.core
 
 /**
- * Copyright (c) 2020-2023 Gerhard Muth
+ * Copyright (c) 2020-2024 Gerhard Muth
  */
 
 import kotlin.test.Test
+import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 
 class IppOperationsTests {
 
     @Test
     fun unknownOperationCodeFails() {
-        assertFailsWith<IppException> {
-            IppOperation.fromInt(0)
-        }
+            val operation = IppOperation.fromInt(0)
+            assertEquals(IppOperation.Unknown, operation)
     }
 
 }
\ No newline at end of file
diff --git a/src/test/kotlin/de/gmuth/ipp/core/IppRequestTests.kt b/src/test/kotlin/de/gmuth/ipp/core/IppRequestTests.kt
index 77629a7a..8b7a5bb9 100644
--- a/src/test/kotlin/de/gmuth/ipp/core/IppRequestTests.kt
+++ b/src/test/kotlin/de/gmuth/ipp/core/IppRequestTests.kt
@@ -37,11 +37,11 @@ class IppRequestTests {
         assertEquals("2.0", request.version)
         assertEquals(IppOperation.StartupPrinter, request.operation)
         assertEquals(Charsets.UTF_8, request.attributesCharset)
-        assertEquals("en-us", request.operationGroup.getValue("attributes-natural-language"))
+        assertEquals("en", request.operationGroup.getValue("attributes-natural-language"))
         assertEquals("ipp://foo", request.printerOrJobUri.toString())
         assertEquals("Startup-Printer", request.codeDescription)
         val requestEncoded = request.encode()
-        assertEquals(100, requestEncoded.size)
+        assertEquals(97, requestEncoded.size)
     }
 
     @Test
@@ -64,7 +64,7 @@ class IppRequestTests {
             assertNotNull(operationGroup)
             operationGroup.run {
                 assertEquals(Charsets.UTF_8, getValue("attributes-charset"))
-                assertEquals("en-us", getValue("attributes-natural-language"))
+                assertEquals("en", getValue("attributes-natural-language"))
                 assertEquals(URI.create("ipp://printer"), getValue("printer-uri"))
             }
             assertEquals(listOf("one", "two"), requestedAttributes)