diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 7c28a8800e8..f49c7c0b210 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -112,6 +112,10 @@ Bug Fixes
   seek/lookup which can cause sideeffects if done on a cached FST root arc.
   (Simon Willnauer)
 
+* LUCENE-5161: Fix default chunk sizes in FSDirectory.java to not be unnecessarily large,
+  and fix setReadChunkSize to always work regardless of whether the machine is 32bit
+  or 64bit.  (Uwe Schindler, Robert Muir)
+
 API Changes
 
 * LUCENE-5094: Add ramBytesUsed() to MultiDocValues.OrdinalMap.
diff --git a/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java b/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
index 1c739bd2831..33b99845287 100644
--- a/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
@@ -112,12 +112,9 @@ import org.apache.lucene.util.Constants;
 public abstract class FSDirectory extends Directory {
 
   /**
-   * Default read chunk size.  This is a conditional default: on 32bit JVMs, it defaults to 100 MB.  On 64bit JVMs, it's
-   * <code>Integer.MAX_VALUE</code>.
-   *
-   * @see #setReadChunkSize
+   * Default read chunk size: 2*{@link BufferedIndexInput#MERGE_BUFFER_SIZE}.
    */
-  public static final int DEFAULT_READ_CHUNK_SIZE = Constants.JRE_IS_64BIT ? Integer.MAX_VALUE : 100 * 1024 * 1024;
+  public static final int DEFAULT_READ_CHUNK_SIZE = BufferedIndexInput.MERGE_BUFFER_SIZE * 2;
 
   protected final File directory; // The underlying filesystem directory
   protected final Set<String> staleFiles = synchronizedSet(new HashSet<String>()); // Files written, but not yet sync'ed
@@ -370,20 +367,13 @@ public abstract class FSDirectory extends Directory {
    * already-opened {@link IndexInput}s.  You should call
    * this before attempting to open an index on the
    * directory.</p>
-   *
-   * <p> <b>NOTE</b>: This value should be as large as
-   * possible to reduce any possible performance impact.  If
-   * you still encounter an incorrect OutOfMemoryError,
-   * trying lowering the chunk size.</p>
    */
   public final void setReadChunkSize(int chunkSize) {
     // LUCENE-1566
     if (chunkSize <= 0) {
       throw new IllegalArgumentException("chunkSize must be positive");
     }
-    if (!Constants.JRE_IS_64BIT) {
-      this.chunkSize = chunkSize;
-    }
+    this.chunkSize = chunkSize;
   }
 
   /**
diff --git a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
index 985c1d205e7..90fc51b7458 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
@@ -20,6 +20,7 @@ package org.apache.lucene.util;
 import java.io.*;
 import java.lang.annotation.*;
 import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.*;
 import java.util.concurrent.*;
@@ -1135,9 +1136,10 @@ public abstract class LuceneTestCase extends Assert {
     FSDirectory d = null;
     try {
       d = CommandLineUtil.newFSDirectory(clazz, file);
-    } catch (Exception e) {
-      d = FSDirectory.open(file);
+    } catch (NoSuchMethodException | InstantiationException | IllegalAccessException | InvocationTargetException e) {
+      Rethrow.rethrow(e);
     }
+    d.setReadChunkSize(_TestUtil.nextInt(random(), 8, 32678));
     return d;
   }