Index: lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 1301045)
+++ lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -1801,4 +1801,21 @@
     w.close();
     dir.close();
   }
+
+  // LUCENE-3872
+  public void testPrepareCommitThenClose() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriter w = new IndexWriter(dir,
+                                    new IndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random)));
+
+    w.prepareCommit();
+    // missing call:
+    // w.commit();
+    w.addDocument(new Document());
+    w.close();
+    IndexReader r = IndexReader.open(dir);
+    assertEquals(1, r.maxDoc());
+    r.close();
+    dir.close();
+  }
 }
Index: lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1301045)
+++ lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -2358,7 +2358,7 @@
    *  #rollback()} to revert the commit and undo all changes
    *  done since the writer was opened.</p>
    *
-   *  You can also just call {@link #commit(Map)} directly
+   *  <p>You can also just call {@link #commit(Map)} directly
    *  without prepareCommit first in which case that method
    *  will internally call prepareCommit.
    *