diff --git a/core/src/main/scala/org/apache/spark/SparkConf.scala b/core/src/main/scala/org/apache/spark/SparkConf.scala
index 4c6c86c7bad78b74ef8d9c4fba323fc7684665eb..c14764f7739822d8b967d53f8c9ea3aa2e0e78b1 100644
--- a/core/src/main/scala/org/apache/spark/SparkConf.scala
+++ b/core/src/main/scala/org/apache/spark/SparkConf.scala
@@ -61,7 +61,7 @@ class SparkConf(loadDefaults: Boolean) extends Cloneable with Logging {
       throw new NullPointerException("null key")
     }
     if (value == null) {
-      throw new NullPointerException("null value")
+      throw new NullPointerException("null value for " + key)
     }
     settings(key) = value
     this