diff --git a/xml/src/main/java/org/kxml2/io/KXmlParser.java b/xml/src/main/java/org/kxml2/io/KXmlParser.java
index 2be8d36..80fd8ca 100644
--- a/xml/src/main/java/org/kxml2/io/KXmlParser.java
+++ b/xml/src/main/java/org/kxml2/io/KXmlParser.java
@@ -1612,7 +1612,7 @@
         boolean detectCharset = (charset == null);
 
         if (is == null) {
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("is == null");
         }
 
         try {
diff --git a/xml/src/main/java/org/kxml2/io/KXmlSerializer.java b/xml/src/main/java/org/kxml2/io/KXmlSerializer.java
index d1965d6..8fa2756 100644
--- a/xml/src/main/java/org/kxml2/io/KXmlSerializer.java
+++ b/xml/src/main/java/org/kxml2/io/KXmlSerializer.java
@@ -327,7 +327,7 @@
     public void setOutput(OutputStream os, String encoding)
         throws IOException {
         if (os == null)
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("os == null");
         setOutput(
             encoding == null
                 ? new OutputStreamWriter(os)