Index: lucene/core/src/test/org/apache/lucene/index/TestDirectoryReaderReopen.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestDirectoryReaderReopen.java	(revision 1463662)
+++ lucene/core/src/test/org/apache/lucene/index/TestDirectoryReaderReopen.java	(working copy)
@@ -594,4 +594,28 @@
     r.close();
     dir.close();
   }
+
+  public void testOpenIfChangedNRTToCommit() throws Exception {
+    Directory dir = newDirectory();
+
+    // Can't use RIW because it randomly commits:
+    IndexWriter w = new IndexWriter(dir, newIndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random())));
+    Document doc = new Document();
+    doc.add(newStringField("field", "value", Field.Store.NO));
+    w.addDocument(doc);
+    w.commit();
+    List<IndexCommit> commits = DirectoryReader.listCommits(dir);
+    assertEquals(1, commits.size());
+    w.addDocument(doc);
+    DirectoryReader r = DirectoryReader.open(w, true);
+
+    assertEquals(2, r.numDocs());
+    IndexReader r2 = DirectoryReader.openIfChanged(r, commits.get(0));
+    assertNotNull(r2);
+    r.close();
+    assertEquals(1, r2.numDocs());
+    w.close();
+    r2.close();
+    dir.close();
+  }
 }
Index: lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java	(revision 1463662)
+++ lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java	(working copy)
@@ -260,7 +260,7 @@
 
   private DirectoryReader doOpenFromWriter(IndexCommit commit) throws IOException {
     if (commit != null) {
-      throw new IllegalArgumentException("a reader obtained from IndexWriter.getReader() cannot currently accept a commit");
+      return doOpenFromCommit(commit);
     }
 
     if (writer.nrtIsCurrent(segmentInfos)) {
@@ -293,6 +293,10 @@
       }
     }
 
+    return doOpenFromCommit(commit);
+  }
+
+  private DirectoryReader doOpenFromCommit(IndexCommit commit) throws IOException {
     return (DirectoryReader) new SegmentInfos.FindSegmentsFile(directory) {
       @Override
       protected Object doBody(String segmentFileName) throws IOException {