diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
index 2ed0e40a4c03f..17118499d0c87 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
@@ -102,7 +102,10 @@ case class Cast(child: Expression, dataType: DataType) extends UnaryExpression {
   // Timestamp to long, converting milliseconds to seconds
   private def timestampToLong(ts: Timestamp) = ts.getTime / 1000
 
-  private def timestampToDouble(ts: Timestamp) = ts.getTime.toDouble / 1000
+  private def timestampToDouble(ts: Timestamp) = {
+    // First part is the seconds since the beginning of time, followed by nanosecs.
+    ts.getTime / 1000 + ts.getNanos.toDouble / 1000000000
+  }
 
   def castToLong: Any => Any = child.dataType match {
     case StringType => nullOrCast[String](_, s => try s.toLong catch {
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvaluationSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvaluationSuite.scala
index 510b9e8bcec87..a897040b439e8 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvaluationSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvaluationSuite.scala
@@ -245,14 +245,14 @@ class ExpressionEvaluationSuite extends FunSuite {
   }
 
   test("timestamp casting") {
-    val millis = 15 * 1000 + 1
+    val millis = 15 * 1000 + 2
     val ts = new Timestamp(millis)
     val ts1 = new Timestamp(15 * 1000)  // a timestamp without the milliseconds part
-    checkEvaluation(ts cast ShortType, 15)
-    checkEvaluation(ts cast IntegerType, 15)
-    checkEvaluation(ts cast LongType, 15)
-    checkEvaluation(ts cast FloatType, 15.001f)
-    checkEvaluation(ts cast DoubleType, 15.001)
+    checkEvaluation(Cast(ts, ShortType), 15)
+    checkEvaluation(Cast(ts, IntegerType), 15)
+    checkEvaluation(Cast(ts, LongType), 15)
+    checkEvaluation(Cast(ts, FloatType), 15.002f)
+    checkEvaluation(Cast(ts, DoubleType), 15.002)
     checkEvaluation(Cast(Cast(ts, ShortType), TimestampType), ts1)
     checkEvaluation(Cast(Cast(ts, IntegerType), TimestampType), ts1)
     checkEvaluation(Cast(Cast(ts, LongType), TimestampType), ts1)
@@ -261,6 +261,9 @@ class ExpressionEvaluationSuite extends FunSuite {
     checkEvaluation(Cast(Cast(millis.toDouble / 1000, TimestampType), DoubleType),
       millis.toDouble / 1000)
     checkEvaluation(Cast(Literal(BigDecimal(1)) cast TimestampType, DecimalType), 1)
+
+    // A test for higher precision than millis
+    checkEvaluation(Cast(Cast(0.00000001, TimestampType), DoubleType), 0.00000001)
   }
 }