diff --git a/lucene/test-framework/src/java/org/apache/lucene/tests/util/RamUsageTester.java b/lucene/test-framework/src/java/org/apache/lucene/tests/util/RamUsageTester.java
index f3f6a515e20c..b013ef4b58d3 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/tests/util/RamUsageTester.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/tests/util/RamUsageTester.java
@@ -38,6 +38,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.atomic.LongAdder;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.function.Predicate;
 import java.util.function.ToLongFunction;
@@ -291,6 +292,11 @@ private void init() {
 
               // Ignorable JDK classes.
               a(ByteOrder.class, _ -> 0);
+
+              // For LongAdder, assume it has the size of a single long, as we can't access its
+              // internal fields and it
+              // is designed to be space efficient when not contended.
+              a(LongAdder.class, _ -> Long.SIZE);
             }
 
             @SuppressWarnings("unchecked")