diff --git a/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsReader.java b/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsReader.java
index c9e17033f59..4847017ca80 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsReader.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsReader.java
@@ -89,10 +89,7 @@ public final class BlockTreeTermsReader extends FieldsProducer {
   final static String TERMS_CODEC_NAME = "BlockTreeTermsDict";
 
   /** Initial terms format. */
-  public static final int VERSION_START = 2;
-
-  /** Auto-prefix terms have been superseded by points. */
-  public static final int VERSION_AUTO_PREFIX_TERMS_REMOVED = 3;
+  public static final int VERSION_START = 3;
 
   /** The long[] + byte[] metadata has been replaced with a single byte[]. */
   public static final int VERSION_META_LONGS_REMOVED = 4;
@@ -137,26 +134,17 @@ public final class BlockTreeTermsReader extends FieldsProducer {
       termsIn = state.directory.openInput(termsName, state.context);
       version = CodecUtil.checkIndexHeader(termsIn, TERMS_CODEC_NAME, VERSION_START, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
 
-      if (version < VERSION_AUTO_PREFIX_TERMS_REMOVED) {
-        // pre-6.2 index, records whether auto-prefix terms are enabled in the header
-        byte b = termsIn.readByte();
-        if (b != 0) {
-          throw new CorruptIndexException("Index header pretends the index has auto-prefix terms: " + b, termsIn);
-        }
-      }
-
       String indexName = IndexFileNames.segmentFileName(segment, state.segmentSuffix, TERMS_INDEX_EXTENSION);
       indexIn = state.directory.openInput(indexName, state.context);
       CodecUtil.checkIndexHeader(indexIn, TERMS_INDEX_CODEC_NAME, version, version, state.segmentInfo.getId(), state.segmentSuffix);
-      CodecUtil.checksumEntireFile(indexIn);
 
       // Have PostingsReader init itself
       postingsReader.init(termsIn, state);
-      
-      // NOTE: data file is too costly to verify checksum against all the bytes on open,
-      // but for now we at least verify proper structure of the checksum footer: which looks
-      // for FOOTER_MAGIC + algorithmID. This is cheap and can detect some forms of corruption
-      // such as file truncation.
+
+      // Verifying the checksum against all bytes would be too costly, but for now we at least
+      // verify proper structure of the checksum footer. This is cheap and can detect some forms
+      // of corruption such as file truncation.
+      CodecUtil.retrieveChecksum(indexIn);
       CodecUtil.retrieveChecksum(termsIn);
 
       // Read per-field details
@@ -307,6 +295,9 @@ public final class BlockTreeTermsReader extends FieldsProducer {
 
   @Override
   public void checkIntegrity() throws IOException { 
+    // terms index
+    CodecUtil.checksumEntireFile(indexIn);
+
     // term dictionary
     CodecUtil.checksumEntireFile(termsIn);