diff --git a/spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java b/spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java
index aa843eca83a..1069110f80c 100644
--- a/spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java
+++ b/spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java
@@ -72,6 +72,8 @@ public final class StringDecoder extends AbstractDataBufferDecoder<String> {
 
 	private final boolean stripDelimiter;
 
+	private Charset defaultCharset = DEFAULT_CHARSET;
+
 	private final ConcurrentMap<Charset, byte[][]> delimitersCache = new ConcurrentHashMap<>();
 
 
@@ -83,6 +85,24 @@ public final class StringDecoder extends AbstractDataBufferDecoder<String> {
 	}
 
 
+	/**
+	 * Set the default character set to fall back on if the MimeType does not specify any.
+	 * <p>By default this is {@code UTF-8}.
+	 * @param defaultCharset the charset to fall back on
+	 * @since 5.2.9
+	 */
+	public void setDefaultCharset(Charset defaultCharset) {
+		this.defaultCharset = defaultCharset;
+	}
+
+	/**
+	 * Return the configured {@link #setDefaultCharset(Charset) defaultCharset}.
+	 * @since 5.2.9
+	 */
+	public Charset getDefaultCharset() {
+		return this.defaultCharset;
+	}
+
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		return (elementType.resolve() == String.class && super.canDecode(elementType, mimeType));
@@ -136,12 +156,12 @@ public final class StringDecoder extends AbstractDataBufferDecoder<String> {
 		return value;
 	}
 
-	private static Charset getCharset(@Nullable MimeType mimeType) {
+	private Charset getCharset(@Nullable MimeType mimeType) {
 		if (mimeType != null && mimeType.getCharset() != null) {
 			return mimeType.getCharset();
 		}
 		else {
-			return DEFAULT_CHARSET;
+			return getDefaultCharset();
 		}
 	}
 
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java
index 932ff78a057..4f1a532b98c 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java
@@ -411,7 +411,7 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 
 		try {
 			int status = response.getServletResponse().getStatus();
-			if (status < 200 || status > 299) {
+			if (status < 200 || (status > 299 && status < 400)) {
 				return;
 			}
 		}
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java
index 0e5ef25cd70..c952eb16a6e 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java
@@ -400,6 +400,25 @@ public class RequestResponseBodyMethodProcessorTests {
 		this.servletRequest.removeAttribute(WebUtils.FORWARD_REQUEST_URI_ATTRIBUTE);
 	}
 
+	@Test
+	public void addContentDispositionHeaderToErrorResponse() throws Exception {
+		ContentNegotiationManagerFactoryBean factory = new ContentNegotiationManagerFactoryBean();
+		factory.addMediaType("pdf", new MediaType("application", "pdf"));
+		factory.afterPropertiesSet();
+
+		RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(
+				Collections.singletonList(new StringHttpMessageConverter()),
+				factory.getObject());
+
+		this.servletRequest.setRequestURI("/hello.dataless");
+		this.servletResponse.setStatus(400);
+
+		processor.handleReturnValue("body", this.returnTypeString, this.container, this.request);
+
+		String header = servletResponse.getHeader("Content-Disposition");
+		assertThat(header).isEqualTo("inline;filename=f.txt");
+	}
+
 	@Test
 	public void supportsReturnTypeResponseBodyOnType() throws Exception {
 		Method method = ResponseBodyController.class.getMethod("handle");
@@ -724,10 +743,14 @@ public class RequestResponseBodyMethodProcessorTests {
 
 		String header = servletResponse.getHeader("Content-Disposition");
 		if (expectContentDisposition) {
-			assertThat(header).as("Expected 'Content-Disposition' header. Use case: '" + comment + "'").isEqualTo("inline;filename=f.txt");
+			assertThat(header)
+					.as("Expected 'Content-Disposition' header. Use case: '" + comment + "'")
+					.isEqualTo("inline;filename=f.txt");
 		}
 		else {
-			assertThat(header).as("Did not expect 'Content-Disposition' header. Use case: '" + comment + "'").isNull();
+			assertThat(header)
+					.as("Did not expect 'Content-Disposition' header. Use case: '" + comment + "'")
+					.isNull();
 		}
 
 		this.servletRequest = new MockHttpServletRequest();