diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index c9c97ba847856..3f01983eb7379 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -2339,13 +2339,25 @@ private[spark] class RedirectThread(
  * in a circular buffer. The current contents of the buffer can be accessed using
  * the toString method.
  */
-private[spark] class CircularBuffer(sizeInByte: Int = 10240) extends java.io.OutputStream {
+private[spark] class CircularBuffer(sizeInBytes: Int = 10240) extends java.io.OutputStream {
   var pos: Int = 0
-  var buffer = new Array[Int](sizeInByte / 4)
+  var buffer = new Array[Byte](sizeInBytes)
 
-  def write(i: Int): Unit = {
-    buffer(pos) = i
-    pos = (pos + 1) % buffer.size
+  /**
+   * Writes the specified byte to this output stream. The general
+   * contract for [[write]] is that one byte is written
+   * to the output stream. The byte to be written is the eight
+   * low-order bits of the argument `i`. The 24
+   * high-order bits of `i` are ignored.
+   *
+   * Subclasses of [[OutputStream]] must provide an
+   * implementation for this method.
+   *
+   * @param i the byte to be written.
+   */
+  override def write(i: Int): Unit = {
+    buffer(pos) = i.asInstanceOf[Byte]
+    pos = (pos + 1) % buffer.length
   }
 
   override def toString: String = {
diff --git a/core/src/test/scala/org/apache/spark/util/UtilsSuite.scala b/core/src/test/scala/org/apache/spark/util/UtilsSuite.scala
index a61ea3918f46a..baa4c661cc21e 100644
--- a/core/src/test/scala/org/apache/spark/util/UtilsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/UtilsSuite.scala
@@ -673,4 +673,12 @@ class UtilsSuite extends SparkFunSuite with ResetSystemProperties with Logging {
     assert(!Utils.isInDirectory(nullFile, parentDir))
     assert(!Utils.isInDirectory(nullFile, childFile3))
   }
+
+  test("circular buffer") {
+    val buffer = new CircularBuffer(25)
+    val stream = new java.io.PrintStream(buffer, true, "UTF-8")
+
+    stream.println("test circular test circular test circular test circular test circular")
+    assert(buffer.toString === "t circular test circular\n")
+  }
 }