diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 111055c8b8a2..2f42f3695846 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -174,6 +174,8 @@ Bug Fixes
 
 * GITHUB#13376: Fix integer overflow exception in postings encoding as group-varint. (Zhang Chao, Guo Feng)
 
+* GITHUB#13421: Fixes TestOrdinalMap.testRamBytesUsed for multiple default PackedInts.NullReader instances. (Amir Raza)
+
 Build
 ---------------------
 
diff --git a/lucene/core/src/java/org/apache/lucene/util/packed/PackedLongValues.java b/lucene/core/src/java/org/apache/lucene/util/packed/PackedLongValues.java
index ae7112624340..cda57f0fb4cf 100644
--- a/lucene/core/src/java/org/apache/lucene/util/packed/PackedLongValues.java
+++ b/lucene/core/src/java/org/apache/lucene/util/packed/PackedLongValues.java
@@ -29,7 +29,7 @@ public class PackedLongValues extends LongValues implements Accountable {
   private static final long BASE_RAM_BYTES_USED =
       RamUsageEstimator.shallowSizeOfInstance(PackedLongValues.class);
 
-  static final int DEFAULT_PAGE_SIZE = 256;
+  public static final int DEFAULT_PAGE_SIZE = 256;
   static final int MIN_PAGE_SIZE = 64;
   // More than 1M doesn't really makes sense with these appending buffers
   // since their goal is to try to have small numbers of bits per value
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestOrdinalMap.java b/lucene/core/src/test/org/apache/lucene/index/TestOrdinalMap.java
index faa2aae329f2..d5b3448ffa58 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestOrdinalMap.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestOrdinalMap.java
@@ -30,6 +30,8 @@
 import org.apache.lucene.tests.util.TestUtil;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.LongValues;
+import org.apache.lucene.util.packed.PackedInts;
+import org.apache.lucene.util.packed.PackedLongValues;
 
 public class TestOrdinalMap extends LuceneTestCase {
 
@@ -52,7 +54,9 @@ public long accumulateObject(
             long shallowSize,
             java.util.Map<Field, Object> fieldValues,
             java.util.Collection<Object> queue) {
-          if (o == LongValues.ZEROES || o == LongValues.IDENTITY) {
+          if (o == LongValues.ZEROES
+              || o == LongValues.IDENTITY
+              || o == PackedInts.NullReader.forCount(PackedLongValues.DEFAULT_PAGE_SIZE)) {
             return 0L;
           }
           if (o instanceof OrdinalMap) {