diff --git a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
index 085070d6d1f..c33a805cb15 100644
--- a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
@@ -3363,6 +3363,18 @@ public class IndexWriter implements Closeable, TwoPhaseCommit {
       mergingSegments.add(info);
     }
 
+    assert merge.estimatedMergeBytes == 0;
+    assert merge.totalMergeBytes == 0;
+    for(SegmentInfoPerCommit info : merge.segments) {
+      if (info.info.getDocCount() > 0) {
+        final int delCount = numDeletedDocs(info);
+        assert delCount <= info.info.getDocCount();
+        final double delRatio = ((double) delCount)/info.info.getDocCount();
+        merge.estimatedMergeBytes += info.sizeInBytes() * (1.0 - delRatio);
+        merge.totalMergeBytes += info.sizeInBytes();
+      }
+    }
+
     // Merge is now registered
     merge.registerDone = true;
 
@@ -3451,17 +3463,6 @@ public class IndexWriter implements Closeable, TwoPhaseCommit {
     if (infoStream.isEnabled("IW")) {
       infoStream.message("IW", "merge seg=" + merge.info.info.name + " " + segString(merge.segments));
     }
-
-    assert merge.estimatedMergeBytes == 0;
-    for(SegmentInfoPerCommit info : merge.segments) {
-      if (info.info.getDocCount() > 0) {
-        final int delCount = numDeletedDocs(info);
-        assert delCount <= info.info.getDocCount();
-        final double delRatio = ((double) delCount)/info.info.getDocCount();
-        merge.estimatedMergeBytes += info.sizeInBytes() * (1.0 - delRatio);
-        merge.totalMergeBytes += info.sizeInBytes();
-      }
-    }
   }
 
   static void setDiagnostics(SegmentInfo info, String source) {
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
index e85ec16191f..a90fe6f7f35 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
@@ -365,6 +365,7 @@ public class TestConcurrentMergeScheduler extends LuceneTestCase {
         w.deleteDocuments(new Term("id", ""+random().nextInt(i+1)));
       }
     }
+    assertTrue(((TrackingCMS) iwc.getMergeScheduler()).totMergedBytes != 0);
     w.close();
     d.close();
   }