diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataConfiguration.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataConfiguration.java
index 2a2291bdca..4feca9dba8 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataConfiguration.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataConfiguration.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.data.elasticsearch;
 
+import java.util.Collections;
+
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.action.support.WriteRequest;
 import org.elasticsearch.client.RestHighLevelClient;
@@ -31,6 +33,7 @@ import org.springframework.data.elasticsearch.core.ElasticsearchRestTemplate;
 import org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations;
 import org.springframework.data.elasticsearch.core.ReactiveElasticsearchTemplate;
 import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
+import org.springframework.data.elasticsearch.core.convert.ElasticsearchCustomConversions;
 import org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter;
 import org.springframework.data.elasticsearch.core.mapping.SimpleElasticsearchMappingContext;
 import org.springframework.web.reactive.function.client.WebClient;
@@ -43,6 +46,7 @@ import org.springframework.web.reactive.function.client.WebClient;
  *
  * @author Brian Clozel
  * @author Scott Frederick
+ * @author Stephane Nicoll
  */
 abstract class ElasticsearchDataConfiguration {
 
@@ -51,14 +55,26 @@ abstract class ElasticsearchDataConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean
-		ElasticsearchConverter elasticsearchConverter(SimpleElasticsearchMappingContext mappingContext) {
-			return new MappingElasticsearchConverter(mappingContext);
+		ElasticsearchCustomConversions elasticsearchCustomConversions() {
+			return new ElasticsearchCustomConversions(Collections.emptyList());
+		}
+
+		@Bean
+		@ConditionalOnMissingBean
+		SimpleElasticsearchMappingContext mappingContext(
+				ElasticsearchCustomConversions elasticsearchCustomConversions) {
+			SimpleElasticsearchMappingContext mappingContext = new SimpleElasticsearchMappingContext();
+			mappingContext.setSimpleTypeHolder(elasticsearchCustomConversions.getSimpleTypeHolder());
+			return mappingContext;
 		}
 
 		@Bean
 		@ConditionalOnMissingBean
-		SimpleElasticsearchMappingContext mappingContext() {
-			return new SimpleElasticsearchMappingContext();
+		ElasticsearchConverter elasticsearchConverter(SimpleElasticsearchMappingContext mappingContext,
+				ElasticsearchCustomConversions elasticsearchCustomConversions) {
+			MappingElasticsearchConverter converter = new MappingElasticsearchConverter(mappingContext);
+			converter.setConversions(elasticsearchCustomConversions);
+			return converter;
 		}
 
 	}
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataAutoConfigurationTests.java
index 7a7c0b244d..66d0cc0d9d 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/data/elasticsearch/ElasticsearchDataAutoConfigurationTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,10 @@
 
 package org.springframework.boot.autoconfigure.data.elasticsearch;
 
+import java.math.BigDecimal;
+import java.util.Collections;
+
+import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -25,9 +29,13 @@ import org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestCli
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.data.elasticsearch.core.ElasticsearchRestTemplate;
 import org.springframework.data.elasticsearch.core.ReactiveElasticsearchTemplate;
 import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
+import org.springframework.data.elasticsearch.core.convert.ElasticsearchCustomConversions;
+import org.springframework.data.elasticsearch.core.mapping.SimpleElasticsearchMappingContext;
+import org.springframework.data.mapping.model.SimpleTypeHolder;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
@@ -40,10 +48,11 @@ import static org.mockito.Mockito.mock;
  * @author Brian Clozel
  * @author Peter-Josef Meisch
  * @author Scott Frederick
+ * @author Stephane Nicoll
  */
 class ElasticsearchDataAutoConfigurationTests {
 
-	private ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
 			.withConfiguration(AutoConfigurations.of(ElasticsearchRestClientAutoConfiguration.class,
 					ReactiveElasticsearchRestClientAutoConfiguration.class, ElasticsearchDataAutoConfiguration.class));
 
@@ -61,7 +70,26 @@ class ElasticsearchDataAutoConfigurationTests {
 	void defaultRestBeansRegistered() {
 		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(ElasticsearchRestTemplate.class)
 				.hasSingleBean(ReactiveElasticsearchTemplate.class).hasSingleBean(ElasticsearchConverter.class)
-				.hasSingleBean(ElasticsearchConverter.class));
+				.hasSingleBean(ElasticsearchConverter.class).hasSingleBean(ElasticsearchCustomConversions.class));
+	}
+
+	@Test
+	void defaultConversionsRegisterBigDecimalAsSimpleType() {
+		this.contextRunner.run((context) -> {
+			SimpleElasticsearchMappingContext mappingContext = context.getBean(SimpleElasticsearchMappingContext.class);
+			assertThat(mappingContext)
+					.extracting("simpleTypeHolder", InstanceOfAssertFactories.type(SimpleTypeHolder.class)).satisfies(
+							(simpleTypeHolder) -> assertThat(simpleTypeHolder.isSimpleType(BigDecimal.class)).isTrue());
+		});
+	}
+
+	@Test
+	void customConversionsShouldBeUsed() {
+		this.contextRunner.withUserConfiguration(CustomElasticsearchCustomConversions.class).run((context) -> {
+			assertThat(context).hasSingleBean(ElasticsearchCustomConversions.class).hasBean("testCustomConversions");
+			assertThat(context.getBean(ElasticsearchConverter.class).getConversionService()
+					.canConvert(ElasticsearchRestTemplate.class, Boolean.class)).isTrue();
+		});
 	}
 
 	@Test
@@ -77,6 +105,16 @@ class ElasticsearchDataAutoConfigurationTests {
 						.contains("reactiveElasticsearchTemplate"));
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class CustomElasticsearchCustomConversions {
+
+		@Bean
+		ElasticsearchCustomConversions testCustomConversions() {
+			return new ElasticsearchCustomConversions(Collections.singletonList(new MyConverter()));
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class CustomRestTemplate {
 
@@ -97,4 +135,13 @@ class ElasticsearchDataAutoConfigurationTests {
 
 	}
 
+	static class MyConverter implements Converter<ElasticsearchRestTemplate, Boolean> {
+
+		@Override
+		public Boolean convert(ElasticsearchRestTemplate source) {
+			return null;
+		}
+
+	}
+
 }