diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 1cc811449f5..2a8558e9a9a 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -109,6 +109,9 @@ New Features
 * SOLR-4114: Allow creating more than one shard per instance with the
   Collection API. (Per Steffensen, Mark Miller)
 
+* SOLR-3531: Allowing configuring maxMergeSizeMB and maxCachedMB when
+  using NRTCachingDirectoryFactory. (Andy Laird via Mark Miller) 
+
 Optimizations
 ----------------------
 
diff --git a/solr/core/src/java/org/apache/solr/core/NRTCachingDirectoryFactory.java b/solr/core/src/java/org/apache/solr/core/NRTCachingDirectoryFactory.java
index 957d3a26361..f97c2ee2925 100644
--- a/solr/core/src/java/org/apache/solr/core/NRTCachingDirectoryFactory.java
+++ b/solr/core/src/java/org/apache/solr/core/NRTCachingDirectoryFactory.java
@@ -23,15 +23,32 @@ import java.io.IOException;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FSDirectory;
 import org.apache.lucene.store.NRTCachingDirectory;
+import org.apache.solr.common.params.SolrParams;
+import org.apache.solr.common.util.NamedList;
 
 /**
  * Factory to instantiate {@link org.apache.lucene.store.NRTCachingDirectory}
  */
 public class NRTCachingDirectoryFactory extends StandardDirectoryFactory {
+  private double maxMergeSizeMB;
+  private double maxCachedMB;
+
+  @Override
+  public void init(NamedList args) {
+    SolrParams params = SolrParams.toSolrParams(args);
+    maxMergeSizeMB = params.getDouble("maxMergeSizeMB", 4);
+    if (maxMergeSizeMB <= 0){
+      throw new IllegalArgumentException("maxMergeSizeMB must be greater than 0");
+    }
+    maxCachedMB = params.getDouble("maxCachedMB", 48);
+    if (maxCachedMB <= 0){
+      throw new IllegalArgumentException("maxCachedMB must be greater than 0");
+    }
+  }
 
   @Override
   protected Directory create(String path) throws IOException {
-    return new NRTCachingDirectory(FSDirectory.open(new File(path)), 4, 48);
+    return new NRTCachingDirectory(FSDirectory.open(new File(path)), maxMergeSizeMB, maxCachedMB);
   }
 
 }