diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala
index dcded0774180eb806674aa4fd848c00a7abb59a6..420303408451f4e8dda5c1f6060888b6b1d4d285 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala
@@ -81,8 +81,12 @@ trait CaseConversionExpression {
   def dataType: DataType = StringType
 
   override def eval(input: Row): Any = {
-    val converted = child.eval(input)
-    convert(converted.toString)
+    val evaluated = child.eval(input)
+    if (evaluated == null) {
+      null
+    } else {
+      convert(evaluated.toString)
+    }
   }
 }
 
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
index 95860e6683f67348ea583b3b32e59d30080dcdce..e2ad3915d31343a328f7726918e18c63dbcc3b89 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
@@ -322,6 +322,13 @@ class SQLQuerySuite extends QueryTest {
         (2, "B"),
         (3, "C"),
         (4, "D")))
+
+    checkAnswer(
+      sql("SELECT n, UPPER(s) FROM nullStrings"),
+      Seq(
+        (1, "ABC"),
+        (2, "ABC"),
+        (3, null)))
   }
     
   test("system function lower()") {
@@ -334,6 +341,13 @@ class SQLQuerySuite extends QueryTest {
         (4, "d"),
         (5, "e"),
         (6, "f")))
+
+    checkAnswer(
+      sql("SELECT n, LOWER(s) FROM nullStrings"),
+      Seq(
+        (1, "abc"),
+        (2, "abc"),
+        (3, null)))
   }  
   
 }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/TestData.scala b/sql/core/src/test/scala/org/apache/spark/sql/TestData.scala
index 944f520e43515ea47d8a6c79250fa2d5c47f73e7..876bd1636aab3ac63955e1b5da51efd404af6a51 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/TestData.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/TestData.scala
@@ -106,4 +106,12 @@ object TestData {
       NullInts(null) :: Nil
     )
   nullInts.registerAsTable("nullInts")
+
+  case class NullStrings(n: Int, s: String)
+  val nullStrings =
+    TestSQLContext.sparkContext.parallelize(
+      NullStrings(1, "abc") ::
+      NullStrings(2, "ABC") ::
+      NullStrings(3, null) :: Nil)
+  nullStrings.registerAsTable("nullStrings")
 }