diff --git a/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/NativeIO.c b/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/NativeIO.c
index afa4720e507..56f0f71eb5a 100644
--- a/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/NativeIO.c
+++ b/hadoop-common-project/hadoop-common/src/main/native/src/org/apache/hadoop/io/nativeio/NativeIO.c
@@ -363,6 +363,15 @@ Java_org_apache_hadoop_io_nativeio_NativeIO_00024POSIX_sync_1file_1range(
 #endif
 }
 
+#define CHECK_DIRECT_BUFFER_ADDRESS(buf) \
+  { \
+    if (!buf) { \
+      THROW(env, "java/lang/UnsupportedOperationException", \
+        "JNI access to direct buffers not available"); \
+      return; \
+    } \
+  }
+
 /**
  * public static native void mlock_native(
  *   ByteBuffer buffer, long offset);
@@ -379,6 +388,7 @@ Java_org_apache_hadoop_io_nativeio_NativeIO_00024POSIX_mlock_1native(
   PASS_EXCEPTIONS(env);
 
   if (mlock(buf, len)) {
+    CHECK_DIRECT_BUFFER_ADDRESS(buf);
     throw_ioe(env, errno);
   }
 }
@@ -399,6 +409,7 @@ Java_org_apache_hadoop_io_nativeio_NativeIO_00024POSIX_munlock_1native(
   PASS_EXCEPTIONS(env);
 
   if (munlock(buf, len)) {
+    CHECK_DIRECT_BUFFER_ADDRESS(buf);
     throw_ioe(env, errno);
   }
 }
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/nativeio/TestNativeIO.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/nativeio/TestNativeIO.java
index 69c963f2d75..917532e4bf8 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/nativeio/TestNativeIO.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/nativeio/TestNativeIO.java
@@ -545,9 +545,12 @@ public class TestNativeIO {
       bufSum += buf[i];
     }
     FileOutputStream fos = new FileOutputStream(TEST_FILE);
-    fos.write(buf);
-    fos.getChannel().force(true);
-    fos.close();
+    try {
+      fos.write(buf);
+      fos.getChannel().force(true);
+    } finally {
+      fos.close();
+    }
     
     FileInputStream fis = null;
     FileChannel channel = null;
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt
index 1b42824e18d..0505fa7dfcb 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt
@@ -42,3 +42,5 @@ HDFS-4949 (Unreleased)
 
     HDFS-5198. NameNodeRpcServer must not send back DNA_FINALIZE in reply to a
     cache report.  (Contributed by Colin Patrick McCabe)
+
+    HDFS-5195. Prevent passing null pointer to mlock and munlock. (cnauroth)