diff --git a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReverseIndexConstructor.java b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReverseIndexConstructor.java
index 32a46f5e..259b5c16 100644
--- a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReverseIndexConstructor.java
+++ b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReverseIndexConstructor.java
@@ -56,10 +56,11 @@ public class ReverseIndexConstructor {
         List<ReversePreindex> merged = new ArrayList<>();
 
         while (toMerge.size() != 1) {
-            for (int i = 0; i < toMerge.size(); i+=2) {
+            for (int i = 0; i + 1< toMerge.size(); i+=2) {
                 var left = toMerge.get(i);
                 var right = toMerge.get(i+1);
 
+                logger.info("Merge {}, {}", i, i+1);
                 merged.add(ReversePreindex.merge(workDir, left, right));
 
                 left.delete();
diff --git a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindex.java b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindex.java
index 3ce189f2..e5e1a5c2 100644
--- a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindex.java
+++ b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindex.java
@@ -38,7 +38,6 @@ public class ReversePreindex {
         IndexSizeEstimator sizeEstimator = new IndexSizeEstimator(ReverseIndexParameters.docsBTreeContext, 2);
         offsets.fold(0, 0, offsets.size(), sizeEstimator);
 
-        System.out.println("size estimate = " + sizeEstimator.size);
         // Write the docs file
         LongArray finalDocs = LongArray.mmapForWriting(outputFileDocs, sizeEstimator.size);
         try (var intermediateDocChannel = documents.createDocumentsFileChannel()) {
@@ -48,6 +47,8 @@ public class ReversePreindex {
 
         LongArray wordIds = segments.wordIds;
 
+        assert offsets.size() == wordIds.size() : "Offsets and word-ids of different size";
+
         // Estimate the size of the words index data
         long wordsSize = ReverseIndexParameters.wordsBTreeContext.calculateSize((int) offsets.size());
 
@@ -108,7 +109,7 @@ public class ReversePreindex {
                 0, left.wordIds.size(),
                 0, right.wordIds.size());
 
-        LongArray counts = LongArray.mmapForWriting(segmentCountsFile, 8*segmentsSize);
+        LongArray counts = LongArray.mmapForWriting(segmentCountsFile, segmentsSize);
 
         return new ReversePreindexWordSegments(wordIdsFile, counts, segmentWordsFile, segmentCountsFile);
     }
@@ -177,6 +178,8 @@ public class ReversePreindex {
 
         mergedDocuments = shrinkMergedDocuments(mergedDocuments, docsFile, 2 * mergingSegment.totalSize());
 
+        mergingSegment.force();
+
         return new ReversePreindex(
                 mergingSegment,
                 new ReversePreindexDocuments(mergedDocuments, docsFile)
diff --git a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindexWordSegments.java b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindexWordSegments.java
index 1bfe90a8..5a0e8f2d 100644
--- a/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindexWordSegments.java
+++ b/code/features-index/index-reverse/src/main/java/nu/marginalia/index/construction/ReversePreindexWordSegments.java
@@ -28,6 +28,8 @@ public class ReversePreindexWordSegments {
                                        Path wordsFile,
                                        Path countsFile)
     {
+        assert wordIds.size() == counts.size();
+
         this.wordIds = wordIds;
         this.counts = counts;
         this.wordsFile = wordsFile;
@@ -97,6 +99,11 @@ public class ReversePreindexWordSegments {
         Files.delete(wordsFile);
     }
 
+    public void force() {
+        counts.force();
+        wordIds.force();
+    }
+
     public class SegmentIterator {
         private final int recordSize;
         private final long fileSize;