diff --git a/src/main/java/org/json/JSONObject.java b/src/main/java/org/json/JSONObject.java
index e7ca7355194be80f2f748432ac88811de4515200..4e03b5a2a2573b10bbd090cff3cd720b3ec6c04d 100644
--- a/src/main/java/org/json/JSONObject.java
+++ b/src/main/java/org/json/JSONObject.java
@@ -131,7 +131,7 @@ public class JSONObject {
              */
             String key = (String) entry.getKey();
             if (key == null) {
-                throw new NullPointerException();
+                throw new NullPointerException("key == null");
             }
             nameValuePairs.put(key, entry.getValue());
         }
diff --git a/src/main/java/org/json/JSONTokener.java b/src/main/java/org/json/JSONTokener.java
index ebfabe47e51c0d1e0a4c63b945192ba316e4f623..202e2e6c8d00b2e917aecf40b27e1abb0f4c8c5c 100644
--- a/src/main/java/org/json/JSONTokener.java
+++ b/src/main/java/org/json/JSONTokener.java
@@ -543,7 +543,7 @@ public class JSONTokener {
      */
     public String nextTo(String excluded) {
         if (excluded == null) {
-            throw new NullPointerException();
+            throw new NullPointerException("excluded == null");
         }
         return nextToInternal(excluded).trim();
     }