diff --git a/lucene/core/src/test/org/apache/lucene/index/TestBackwardsCompatibility.java b/lucene/core/src/test/org/apache/lucene/index/TestBackwardsCompatibility.java
index 5cc5cc18f8e..40885cd444d 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestBackwardsCompatibility.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestBackwardsCompatibility.java
@@ -561,7 +561,10 @@ public class TestBackwardsCompatibility extends LuceneTestCase {
       Directory dir = newFSDirectory(outputDir);
 
       LogMergePolicy mergePolicy = newLogMergePolicy(true, 10);
-      mergePolicy.setNoCFSRatio(1); // This test expects all of its segments to be in CFS
+      
+      // This test expects all of its segments to be in CFS:
+      mergePolicy.setNoCFSRatio(1.0); 
+      mergePolicy.setMaxCFSSegmentSizeMB(Double.POSITIVE_INFINITY);
 
       IndexWriter writer = new IndexWriter(
           dir,