diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/LegacyHealthEndpointCompatibilityConfiguration.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/LegacyHealthEndpointCompatibilityConfiguration.java
index 0c5b32ff2ec..4c1b1add27d 100644
--- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/LegacyHealthEndpointCompatibilityConfiguration.java
+++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/LegacyHealthEndpointCompatibilityConfiguration.java
@@ -16,7 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.health;
 
-import io.micrometer.shaded.reactor.core.publisher.Mono;
+import reactor.core.publisher.Mono;
 
 import org.springframework.boot.actuate.health.HealthAggregator;
 import org.springframework.boot.actuate.health.HealthContributorRegistry;
diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointAutoConfigurationTests.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointAutoConfigurationTests.java
index ca1986172a5..a56ce593454 100644
--- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointAutoConfigurationTests.java
@@ -44,9 +44,11 @@ import org.springframework.boot.actuate.health.NamedContributor;
 import org.springframework.boot.actuate.health.ReactiveHealthContributorRegistry;
 import org.springframework.boot.actuate.health.ReactiveHealthEndpointWebExtension;
 import org.springframework.boot.actuate.health.ReactiveHealthIndicator;
+import org.springframework.boot.actuate.health.ReactiveHealthIndicatorRegistry;
 import org.springframework.boot.actuate.health.Status;
 import org.springframework.boot.actuate.health.StatusAggregator;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -293,6 +295,17 @@ class HealthEndpointAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void runWhenReactorAvailableCreatesReactiveHealthIndicatorRegistryBean() {
+		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(ReactiveHealthIndicatorRegistry.class));
+	}
+
+	@Test // gh-18570
+	void runWhenReactorUnavailableDoesNotCreateReactiveHealthIndicatorRegistryBean() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader(Mono.class.getPackage().getName()))
+				.run((context) -> assertThat(context).doesNotHaveBean(ReactiveHealthIndicatorRegistry.class));
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class HealthIndicatorsConfiguration {
 
diff --git a/src/checkstyle/checkstyle.xml b/src/checkstyle/checkstyle.xml
index 809f7de36c9..d62504d927f 100644
--- a/src/checkstyle/checkstyle.xml
+++ b/src/checkstyle/checkstyle.xml
@@ -13,7 +13,7 @@
 			name="com.puppycrawl.tools.checkstyle.checks.imports.IllegalImportCheck">
 			<property name="regexp" value="true" />
 			<property name="illegalPkgs"
-				value="^sun.*, ^org\.apache\.commons\.(?!compress|dbcp2|lang|lang3|logging|pool2).*, ^com\.google\.common.*, ^org\.flywaydb\.core\.internal.*, ^org\.testcontainers\.shaded.*" />
+				value="^sun.*, ^org\.apache\.commons\.(?!compress|dbcp2|lang|lang3|logging|pool2).*, ^com\.google\.common.*, ^io\.micrometer\.shaded.*, ^org\.flywaydb\.core\.internal.*, ^org\.testcontainers\.shaded.*" />
 			<property name="illegalClasses"
 				value="^com\.hazelcast\.util\.Base64, ^org\.junit\.rules\.ExpectedException, ^org\.mockito\.InjectMocks, ^org\.slf4j\.LoggerFactory, ^reactor\.core\.support\.Assert" />
 		</module>