diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.java
index 96c3db64b7..255f69751c 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.java
@@ -30,12 +30,13 @@ import org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration;
 import org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration.NotReactiveWebApplicationCondition;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration;
-import org.springframework.boot.autoconfigure.web.ServerProperties;
-import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.context.properties.bind.Binder;
+import org.springframework.boot.web.servlet.server.Encoding;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
+import org.springframework.core.env.Environment;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 
@@ -71,14 +72,13 @@ public class HttpMessageConvertersAutoConfiguration {
 
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(StringHttpMessageConverter.class)
-	@EnableConfigurationProperties(ServerProperties.class)
 	protected static class StringHttpMessageConverterConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean
-		public StringHttpMessageConverter stringHttpMessageConverter(ServerProperties serverProperties) {
-			StringHttpMessageConverter converter = new StringHttpMessageConverter(
-					serverProperties.getServlet().getEncoding().getCharset());
+		public StringHttpMessageConverter stringHttpMessageConverter(Environment environment) {
+			Encoding encoding = Binder.get(environment).bindOrCreate("server.servlet.encoding", Encoding.class);
+			StringHttpMessageConverter converter = new StringHttpMessageConverter(encoding.getCharset());
 			converter.setWriteAcceptCharset(false);
 			return converter;
 		}
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfigurationTests.java
index 4b8286d986..f850fe9a60 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfigurationTests.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.http;
 
+import java.nio.charset.StandardCharsets;
+
 import javax.json.bind.Jsonb;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -28,6 +30,7 @@ import org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration;
 import org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration.MappingJackson2HttpMessageConverterConfiguration;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
@@ -237,6 +240,38 @@ class HttpMessageConvertersAutoConfigurationTests {
 				.run((context) -> assertThat(context).doesNotHaveBean(HttpMessageConverters.class));
 	}
 
+	@Test
+	void whenEncodingCharsetIsNotConfiguredThenStringMessageConverterUsesUtf8() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.run((context) -> {
+					assertThat(context).hasSingleBean(StringHttpMessageConverter.class);
+					assertThat(context.getBean(StringHttpMessageConverter.class).getDefaultCharset())
+							.isEqualTo(StandardCharsets.UTF_8);
+				});
+	}
+
+	@Test
+	void whenEncodingCharsetIsConfiguredThenStringMessageConverterUsesSpecificCharset() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.withPropertyValues("server.servlet.encoding.charset=UTF-16").run((context) -> {
+					assertThat(context).hasSingleBean(StringHttpMessageConverter.class);
+					assertThat(context.getBean(StringHttpMessageConverter.class).getDefaultCharset())
+							.isEqualTo(StandardCharsets.UTF_16);
+				});
+	}
+
+	@Test // gh-21789
+	void whenAutoConfigurationIsActiveThenServerPropertiesConfigurationPropertiesAreNotEnabled() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.run((context) -> {
+					assertThat(context).hasSingleBean(HttpMessageConverters.class);
+					assertThat(context).doesNotHaveBean(ServerProperties.class);
+				});
+	}
+
 	private ApplicationContextRunner allOptionsRunner() {
 		return this.contextRunner.withConfiguration(AutoConfigurations.of(GsonAutoConfiguration.class,
 				JacksonAutoConfiguration.class, JsonbAutoConfiguration.class));