diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfiguration.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfiguration.java
index cbf9f303c2..d3a16cdb54 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfiguration.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfiguration.java
@@ -76,8 +76,9 @@ public class MessageSourceAutoConfiguration {
 		}
 		messageSource.setFallbackToSystemLocale(properties.isFallbackToSystemLocale());
 		Duration cacheDuration = properties.getCacheDuration();
-		messageSource.setCacheSeconds(
-				cacheDuration == null ? -1 : (int) cacheDuration.getSeconds());
+		if (cacheDuration != null) {
+			messageSource.setCacheMillis(cacheDuration.toMillis());
+		}
 		messageSource.setAlwaysUseMessageFormat(properties.isAlwaysUseMessageFormat());
 		messageSource.setUseCodeAsDefaultMessage(properties.isUseCodeAsDefaultMessage());
 		return messageSource;
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceProperties.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceProperties.java
index 1935b10f7b..62d366c2cd 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceProperties.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceProperties.java
@@ -19,6 +19,9 @@ package org.springframework.boot.autoconfigure.context;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+
+import org.springframework.boot.convert.DurationUnit;
 
 /**
  * Configuration properties for Message Source.
@@ -44,8 +47,9 @@ public class MessageSourceProperties {
 
 	/**
 	 * Loaded resource bundle files cache duration. When not set, bundles are cached
-	 * forever.
+	 * forever. If a duration suffix is not specified, seconds will be used.
 	 */
+	@DurationUnit(ChronoUnit.SECONDS)
 	private Duration cacheDuration;
 
 	/**
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfigurationTests.java
index 3098a73865..810e765de3 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfigurationTests.java
@@ -23,7 +23,9 @@ import org.junit.Test;
 
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.boot.test.context.runner.ContextConsumer;
 import org.springframework.context.MessageSource;
 import org.springframework.context.MessageSourceResolvable;
 import org.springframework.context.NoSuchMessageException;
@@ -82,6 +84,30 @@ public class MessageSourceAutoConfigurationTests {
 								.isEqualTo("Some text with some swedish öäå!"));
 	}
 
+	@Test
+	public void testCacheDurationNoUnit() {
+		this.contextRunner
+				.withPropertyValues("spring.messages.basename:test/messages",
+						"spring.messages.cache-duration=10")
+				.run(assertCache(10 * 1000));
+	}
+
+	@Test
+	public void testCacheDurationWithUnit() {
+		this.contextRunner
+				.withPropertyValues("spring.messages.basename:test/messages",
+						"spring.messages.cache-duration=1m")
+				.run(assertCache(60 * 1000));
+	}
+
+	private ContextConsumer<AssertableApplicationContext> assertCache(long expected) {
+		return (context) -> {
+			assertThat(assertThat(context).hasSingleBean(MessageSource.class));
+			assertThat(new DirectFieldAccessor(context.getBean(MessageSource.class))
+					.getPropertyValue("cacheMillis")).isEqualTo(expected);
+		};
+	}
+
 	@Test
 	public void testMultipleMessageSourceCreated() {
 		this.contextRunner
diff --git a/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc b/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc
index 4639839df8..8b71c419a0 100644
--- a/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc
+++ b/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc
@@ -123,7 +123,7 @@ content into your application. Rather, pick only the properties that you need.
 	# INTERNATIONALIZATION ({sc-spring-boot-autoconfigure}/context/MessageSourceProperties.{sc-ext}[MessageSourceProperties])
 	spring.messages.always-use-message-format=false # Whether to always apply the MessageFormat rules, parsing even messages without arguments.
 	spring.messages.basename=messages # Comma-separated list of basenames (essentially a fully-qualified classpath location), each following the ResourceBundle convention with relaxed support for slash based locations.
-	spring.messages.cache-duration=-1 # Loaded resource bundle files cache duration. When not set, bundles are cached forever.
+	spring.messages.cache-duration= # Loaded resource bundle files cache duration. When not set, bundles are cached forever. If a duration suffix is not specified, seconds will be used.
 	spring.messages.encoding=UTF-8 # Message bundles encoding.
 	spring.messages.fallback-to-system-locale=true # Whether to fall back to the system Locale if no files for a specific Locale have been found.
 	spring.messages.use-code-as-default-message=false # Whether to use the message code as the default message instead of throwing a "NoSuchMessageException". Recommended during development only.