diff --git a/processing/src/main/java/org/apache/druid/segment/data/CompressionFactory.java b/processing/src/main/java/org/apache/druid/segment/data/CompressionFactory.java
index 0b45cdb8d5cf..10943316b707 100644
--- a/processing/src/main/java/org/apache/druid/segment/data/CompressionFactory.java
+++ b/processing/src/main/java/org/apache/druid/segment/data/CompressionFactory.java
@@ -287,6 +287,11 @@ public interface LongEncodingReader
 
     int read(long[] out, int outPosition, int[] indexes, int length, int indexOffset, int limit);
 
+    /**
+     * Duplicates this reader, creating a new reader that does not share any state. Important to achieve thread-safety,
+     * because a common pattern is to duplicate a reader multiple times and then call {@link #setBuffer} on the
+     * various duplicates.
+     */
     LongEncodingReader duplicate();
   }
 
diff --git a/processing/src/main/java/org/apache/druid/segment/data/LongsLongEncodingReader.java b/processing/src/main/java/org/apache/druid/segment/data/LongsLongEncodingReader.java
index 7fd1aef58b42..2ed0459121af 100644
--- a/processing/src/main/java/org/apache/druid/segment/data/LongsLongEncodingReader.java
+++ b/processing/src/main/java/org/apache/druid/segment/data/LongsLongEncodingReader.java
@@ -69,6 +69,6 @@ public int read(long[] out, int outPosition, int[] indexes, int length, int inde
   @Override
   public CompressionFactory.LongEncodingReader duplicate()
   {
-    return this;
+    return new LongsLongEncodingReader(buffer.getByteBuffer(), buffer.getTypeByteOrder());
   }
 }