diff --git a/CHANGELOG.md b/CHANGELOG.md
index d0ccac007b..03393385ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Removed
 
 ### Fixed
+- Fixed direct serialization of primitive types in `DEFAULT_JSONP_MAPPER` as used by `toJsonString()` ([#1524](https://github.com/opensearch-project/opensearch-java/pull/1524))
 
 ### Security
 
diff --git a/java-client/src/main/java/org/opensearch/client/json/JsonpUtils.java b/java-client/src/main/java/org/opensearch/client/json/JsonpUtils.java
index 8cf51df787..c0d126d0df 100644
--- a/java-client/src/main/java/org/opensearch/client/json/JsonpUtils.java
+++ b/java-client/src/main/java/org/opensearch/client/json/JsonpUtils.java
@@ -43,6 +43,8 @@
 import jakarta.json.stream.JsonParser.Event;
 import jakarta.json.stream.JsonParsingException;
 import java.io.StringReader;
+import java.math.BigDecimal;
+import java.math.BigInteger;
 import java.util.AbstractMap;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -78,11 +80,31 @@ public JsonProvider jsonProvider() {
         public <T> void serialize(T value, JsonGenerator generator) {
             if (value instanceof JsonpSerializable) {
                 ((JsonpSerializable) value).serialize(generator, this);
-                return;
+            } else if (value instanceof JsonValue) {
+                generator.write((JsonValue) value);
+            } else if (value instanceof String) {
+                generator.write((String) value);
+            } else if (value instanceof BigDecimal) {
+                generator.write((BigDecimal) value);
+            } else if (value instanceof BigInteger) {
+                generator.write((BigInteger) value);
+            } else if (value instanceof Short) {
+                generator.write((Short) value);
+            } else if (value instanceof Integer) {
+                generator.write((Integer) value);
+            } else if (value instanceof Long) {
+                generator.write((Long) value);
+            } else if (value instanceof Float) {
+                generator.write((Float) value);
+            } else if (value instanceof Double) {
+                generator.write((Double) value);
+            } else if (value instanceof Boolean) {
+                generator.write((Boolean) value);
+            } else {
+                throw new JsonException(
+                    "Cannot find a serializer for type " + value.getClass().getName() + ". Consider using a full-featured JsonpMapper."
+                );
             }
-            throw new JsonException(
-                "Cannot find a serializer for type " + value.getClass().getName() + ". Consider using a full-featured JsonpMapper."
-            );
         }
 
         @Override
diff --git a/java-client/src/test/java/org/opensearch/client/opensearch/_types/aggregations/ExtendedBoundsTest.java b/java-client/src/test/java/org/opensearch/client/opensearch/_types/aggregations/ExtendedBoundsTest.java
new file mode 100644
index 0000000000..62d5b4b3ab
--- /dev/null
+++ b/java-client/src/test/java/org/opensearch/client/opensearch/_types/aggregations/ExtendedBoundsTest.java
@@ -0,0 +1,21 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.client.opensearch._types.aggregations;
+
+import org.junit.Test;
+import org.opensearch.client.opensearch.model.ModelTestCase;
+
+public class ExtendedBoundsTest extends ModelTestCase {
+    @Test
+    public void testToJsonString() {
+        ExtendedBounds<Double> bounds = ExtendedBounds.of(eb -> eb.min(0.0).max(4096.0));
+
+        assertEquals("{\"max\":4096.0,\"min\":0.0}", bounds.toJsonString());
+    }
+}