diff --git a/module/spring-boot-health/src/main/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointConfiguration.java b/module/spring-boot-health/src/main/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointConfiguration.java
index 9fcf2e59470..43f74c19a8f 100644
--- a/module/spring-boot-health/src/main/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointConfiguration.java
+++ b/module/spring-boot-health/src/main/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointConfiguration.java
@@ -17,6 +17,7 @@
 package org.springframework.boot.health.autoconfigure.actuate.endpoint;
 
 import java.util.Set;
+import java.util.function.BiFunction;
 
 import org.jspecify.annotations.Nullable;
 
@@ -34,6 +35,7 @@ import org.springframework.boot.health.actuate.endpoint.SimpleHttpCodeStatusMapp
 import org.springframework.boot.health.actuate.endpoint.SimpleStatusAggregator;
 import org.springframework.boot.health.actuate.endpoint.StatusAggregator;
 import org.springframework.boot.health.contributor.HealthContributors;
+import org.springframework.boot.health.contributor.ReactiveHealthContributors;
 import org.springframework.boot.health.registry.HealthContributorRegistry;
 import org.springframework.boot.health.registry.ReactiveHealthContributorRegistry;
 import org.springframework.context.ApplicationContext;
@@ -78,8 +80,10 @@ class HealthEndpointConfiguration {
 	@Bean
 	@ConditionalOnBooleanProperty(name = "management.endpoint.health.validate-group-membership", matchIfMissing = true)
 	HealthEndpointGroupMembershipValidator healthEndpointGroupMembershipValidator(HealthEndpointProperties properties,
-			HealthContributorRegistry healthContributorRegistry) {
-		return new HealthEndpointGroupMembershipValidator(properties, healthContributorRegistry);
+			HealthContributorRegistry healthContributorRegistry,
+			ObjectProvider<ReactiveHealthContributorRegistry> reactiveHealthContributorRegistry) {
+		return new HealthEndpointGroupMembershipValidator(properties, healthContributorRegistry,
+				reactiveHealthContributorRegistry.getIfAvailable());
 	}
 
 	@Bean
@@ -138,10 +142,13 @@ class HealthEndpointConfiguration {
 
 		private final HealthContributorRegistry registry;
 
-		HealthEndpointGroupMembershipValidator(HealthEndpointProperties properties,
-				HealthContributorRegistry registry) {
+		@Nullable ReactiveHealthContributorRegistry fallbackRegistry;
+
+		HealthEndpointGroupMembershipValidator(HealthEndpointProperties properties, HealthContributorRegistry registry,
+				@Nullable ReactiveHealthContributorRegistry fallbackRegistry) {
 			this.properties = properties;
 			this.registry = registry;
+			this.fallbackRegistry = fallbackRegistry;
 		}
 
 		@Override
@@ -172,13 +179,28 @@ class HealthEndpointConfiguration {
 		}
 
 		private boolean contributorExists(String[] path) {
+			return contributorExistsInMainRegistry(path) || contributorExistsInFallbackRegistry(path);
+		}
+
+		private boolean contributorExistsInMainRegistry(String[] path) {
+			return contributorExists(path, this.registry, HealthContributors.class, HealthContributors::getContributor);
+		}
+
+		private boolean contributorExistsInFallbackRegistry(String[] path) {
+			return contributorExists(path, this.fallbackRegistry, ReactiveHealthContributors.class,
+					ReactiveHealthContributors::getContributor);
+		}
+
+		@SuppressWarnings("unchecked")
+		private <C> boolean contributorExists(String[] path, @Nullable Object registry, Class<C> collectionType,
+				BiFunction<C, String, Object> getFromCollection) {
 			int pathOffset = 0;
-			Object contributor = this.registry;
+			Object contributor = registry;
 			while (pathOffset < path.length) {
-				if (!(contributor instanceof HealthContributors)) {
+				if (contributor == null || !collectionType.isInstance(contributor)) {
 					return false;
 				}
-				contributor = ((HealthContributors) contributor).getContributor(path[pathOffset]);
+				contributor = getFromCollection.apply((C) contributor, path[pathOffset]);
 				pathOffset++;
 			}
 			return (contributor != null);
diff --git a/module/spring-boot-health/src/test/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointAutoConfigurationTests.java b/module/spring-boot-health/src/test/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointAutoConfigurationTests.java
index 3d0268c1854..960723cbe38 100644
--- a/module/spring-boot-health/src/test/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointAutoConfigurationTests.java
+++ b/module/spring-boot-health/src/test/java/org/springframework/boot/health/autoconfigure/actuate/endpoint/HealthEndpointAutoConfigurationTests.java
@@ -44,6 +44,7 @@ import org.springframework.boot.health.autoconfigure.actuate.endpoint.HealthEndp
 import org.springframework.boot.health.autoconfigure.contributor.HealthContributorAutoConfiguration;
 import org.springframework.boot.health.autoconfigure.registry.HealthContributorRegistryAutoConfiguration;
 import org.springframework.boot.health.contributor.CompositeHealthContributor;
+import org.springframework.boot.health.contributor.CompositeReactiveHealthContributor;
 import org.springframework.boot.health.contributor.Health;
 import org.springframework.boot.health.contributor.HealthContributors;
 import org.springframework.boot.health.contributor.HealthIndicator;
@@ -145,6 +146,20 @@ class HealthEndpointAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void runDoesNotFailWhenHealthEndpointGroupIncludesContributorThatExists() {
+		this.contextRunner.withUserConfiguration(CompositeHealthIndicatorConfiguration.class)
+			.withPropertyValues("management.endpoint.health.group.ready.include=composite/b/c")
+			.run((context) -> assertThat(context).hasNotFailed());
+	}
+
+	@Test // gh-48387
+	void runDoesNotFailWhenHealthEndpointGroupIncludesReactiveContributorThatExists() {
+		this.contextRunner.withUserConfiguration(CompositeReactiveHealthIndicatorConfiguration.class)
+			.withPropertyValues("management.endpoint.health.group.ready.include=composite/b/c")
+			.run((context) -> assertThat(context).hasNotFailed());
+	}
+
 	@Test
 	void runFailsWhenHealthEndpointGroupIncludesContributorThatDoesNotExist() {
 		this.contextRunner.withUserConfiguration(CompositeHealthIndicatorConfiguration.class)
@@ -377,8 +392,27 @@ class HealthEndpointAutoConfigurationTests {
 
 		@Bean
 		CompositeHealthContributor compositeHealthIndicator() {
-			return CompositeHealthContributor.fromMap(Map.of("a", (HealthIndicator) () -> Health.up().build(), "b",
-					CompositeHealthContributor.fromMap(Map.of("c", (HealthIndicator) () -> Health.up().build()))));
+			return CompositeHealthContributor.fromMap(Map.of("a", createHealthIndicator(), "b",
+					CompositeHealthContributor.fromMap(Map.of("c", createHealthIndicator()))));
+		}
+
+		private HealthIndicator createHealthIndicator() {
+			return () -> Health.up().build();
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class CompositeReactiveHealthIndicatorConfiguration {
+
+		@Bean
+		CompositeReactiveHealthContributor compositeHealthIndicator() {
+			return CompositeReactiveHealthContributor.fromMap(Map.of("a", createHealthIndicator(), "b",
+					CompositeReactiveHealthContributor.fromMap(Map.of("c", createHealthIndicator()))));
+		}
+
+		private ReactiveHealthIndicator createHealthIndicator() {
+			return () -> Mono.just(Health.up().build());
 		}
 
 	}