diff --git a/spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java b/spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java
index 568d94b6c03..020a00064c9 100644
--- a/spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java
+++ b/spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java
@@ -134,9 +134,10 @@ public abstract class CoroutinesUtils {
 								Object arg = args[index];
 								if (!(parameter.isOptional() && arg == null)) {
 									KType type = parameter.getType();
-									if (!type.isMarkedNullable() &&
+									if (!(type.isMarkedNullable() && arg == null) &&
 											type.getClassifier() instanceof KClass<?> kClass &&
-											KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass))) {
+											KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass)) &&
+											!JvmClassMappingKt.getJavaClass(kClass).isInstance(arg)) {
 										arg = box(kClass, arg);
 									}
 									argMap.put(parameter, arg);
@@ -166,9 +167,10 @@ public abstract class CoroutinesUtils {
 	private static Object box(KClass<?> kClass, @Nullable Object arg) {
 		KFunction<?> constructor = Objects.requireNonNull(KClasses.getPrimaryConstructor(kClass));
 		KType type = constructor.getParameters().get(0).getType();
-		if (!type.isMarkedNullable() &&
+		if (!(type.isMarkedNullable() && arg == null) &&
 				type.getClassifier() instanceof KClass<?> parameterClass &&
-				KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass))) {
+				KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass)) &&
+				!JvmClassMappingKt.getJavaClass(parameterClass).isInstance(arg)) {
 			arg = box(parameterClass, arg);
 		}
 		if (!KCallablesJvm.isAccessible(constructor)) {
diff --git a/spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt b/spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt
index 4cc2fdeefdb..0f3f4312d2c 100644
--- a/spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt
+++ b/spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt
@@ -236,6 +236,13 @@ class CoroutinesUtilsTests {
 		Assertions.assertThat(mono.awaitSingleOrNull()).isEqualTo("foo")
 	}
 
+	@Test
+	suspend fun invokeSuspendingFunctionWithNullableValueClassParameterAndUnderlyingValue() {
+		val method = CoroutinesUtilsTests::class.java.declaredMethods.first { it.name.startsWith("suspendingFunctionWithNullableValueClass") }
+		val mono = CoroutinesUtils.invokeSuspendingFunction(method, this, "foo", null) as Mono
+		Assertions.assertThat(mono.awaitSingleOrNull()).isEqualTo("foo")
+	}
+
 	@Test
 	suspend fun invokeSuspendingFunctionWithNullableValueClassParameter() {
 		val method = CoroutinesUtilsTests::class.java.declaredMethods.first { it.name.startsWith("suspendingFunctionWithNullableValueClass") }
diff --git a/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java b/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
index 6dca729698e..1a1ef3a011a 100644
--- a/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
+++ b/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
@@ -316,9 +316,10 @@ public class InvocableHandlerMethod extends HandlerMethod {
 						Object arg = args[index];
 						if (!(parameter.isOptional() && arg == null)) {
 							KType type = parameter.getType();
-							if (!type.isMarkedNullable() &&
+							if (!(type.isMarkedNullable() && arg == null) &&
 									type.getClassifier() instanceof KClass<?> kClass &&
-									KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass))) {
+									KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass)) &&
+									!JvmClassMappingKt.getJavaClass(kClass).isInstance(arg)) {
 								arg = box(kClass, arg);
 							}
 							argMap.put(parameter, arg);
@@ -337,9 +338,10 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		private static Object box(KClass<?> kClass, @Nullable Object arg) {
 			KFunction<?> constructor = Objects.requireNonNull(KClasses.getPrimaryConstructor(kClass));
 			KType type = constructor.getParameters().get(0).getType();
-			if (!type.isMarkedNullable() &&
+			if (!(type.isMarkedNullable() && arg == null) &&
 					type.getClassifier() instanceof KClass<?> parameterClass &&
-					KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass))) {
+					KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass)) &&
+					!JvmClassMappingKt.getJavaClass(parameterClass).isInstance(arg)) {
 				arg = box(parameterClass, arg);
 			}
 			if (!KCallablesJvm.isAccessible(constructor)) {
diff --git a/spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt b/spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt
index b7da2b669f2..a3dbd8f91a4 100644
--- a/spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt
+++ b/spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt
@@ -155,6 +155,13 @@ class InvocableHandlerMethodKotlinTests {
 		Assertions.assertThat(value).isEqualTo(1L)
 	}
 
+	@Test
+	fun valueClassWithNullableAndUnderlyingValue() {
+		composite.addResolver(StubArgumentResolver(LongValueClass::class.java, 1L))
+		val value = getInvocable(ValueClassHandler::valueClassWithNullable.javaMethod!!).invokeForRequest(request, null)
+		Assertions.assertThat(value).isEqualTo(1L)
+	}
+
 	@Test
 	fun valueClassWithNullable() {
 		composite.addResolver(StubArgumentResolver(LongValueClass::class.java, null))
@@ -215,6 +222,14 @@ class InvocableHandlerMethodKotlinTests {
 		StepVerifier.create(value as Mono<Long>).verifyComplete()
 	}
 
+	@Test
+	fun suspendingValueClassWithNullableAndUnderlyingValue() {
+		composite.addResolver(ContinuationHandlerMethodArgumentResolver())
+		composite.addResolver(StubArgumentResolver(LongValueClass::class.java, 1L))
+		val value = getInvocable(SuspendingValueClassHandler::valueClassWithNullable.javaMethod!!).invokeForRequest(request, null)
+		StepVerifier.create(value as Mono<Long>).expectNext(1L).verifyComplete()
+	}
+
 	@Test
 	fun suspendingValueClassWithPrivateConstructor() {
 		composite.addResolver(ContinuationHandlerMethodArgumentResolver())
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
index c06ea62a2aa..11e312bbe8b 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
@@ -356,9 +356,10 @@ public class InvocableHandlerMethod extends HandlerMethod {
 							Object arg = args[index];
 							if (!(parameter.isOptional() && arg == null)) {
 								KType type = parameter.getType();
-								if (!type.isMarkedNullable() &&
+								if (!(type.isMarkedNullable() && arg == null) &&
 										type.getClassifier() instanceof KClass<?> kClass &&
-										KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass))) {
+										KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass)) &&
+										!JvmClassMappingKt.getJavaClass(kClass).isInstance(arg)) {
 									arg = box(kClass, arg);
 								}
 								argMap.put(parameter, arg);
@@ -378,9 +379,10 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		private static Object box(KClass<?> kClass, @Nullable Object arg) {
 			KFunction<?> constructor = Objects.requireNonNull(KClasses.getPrimaryConstructor(kClass));
 			KType type = constructor.getParameters().get(0).getType();
-			if (!type.isMarkedNullable() &&
+			if (!(type.isMarkedNullable() && arg == null) &&
 					type.getClassifier() instanceof KClass<?> parameterClass &&
-					KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass))) {
+					KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass)) &&
+					!JvmClassMappingKt.getJavaClass(parameterClass).isInstance(arg)) {
 				arg = box(parameterClass, arg);
 			}
 			if (!KCallablesJvm.isAccessible(constructor)) {
diff --git a/spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/InvocableHandlerMethodKotlinTests.kt b/spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/InvocableHandlerMethodKotlinTests.kt
index 9e41a222399..f8041148619 100644
--- a/spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/InvocableHandlerMethodKotlinTests.kt
+++ b/spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/InvocableHandlerMethodKotlinTests.kt
@@ -258,6 +258,14 @@ class InvocableHandlerMethodKotlinTests {
 		assertHandlerResultValue(result, "1")
 	}
 
+	@Test
+	fun valueClassWithNullableAndUnderlyingValue() {
+		this.resolvers.add(stubResolver(1L, LongValueClass::class.java))
+		val method = ValueClassController::valueClassWithNullable.javaMethod!!
+		val result = invoke(ValueClassController(), method)
+		assertHandlerResultValue(result, "1")
+	}
+
 	@Test
 	fun valueClassWithNullable() {
 		this.resolvers.add(stubResolver(null, LongValueClass::class.java))
@@ -320,6 +328,14 @@ class InvocableHandlerMethodKotlinTests {
 		assertHandlerResultValue(result, "null")
 	}
 
+	@Test
+	fun suspendingValueClassWithNullableAndUnderlyingValue() {
+		this.resolvers.add(stubResolver(1L, LongValueClass::class.java))
+		val method = SuspendingValueClassController::valueClassWithNullable.javaMethod!!
+		val result = invoke(SuspendingValueClassController(), method)
+		assertHandlerResultValue(result, "1")
+	}
+
 	@Test
 	fun suspendingValueClassWithPrivateConstructor() {
 		this.resolvers.add(stubResolver(1L, Long::class.java))
@@ -590,4 +606,4 @@ class InvocableHandlerMethodKotlinTests {
 	}
 
 	class CustomException(message: String) : Throwable(message)
-}
\ No newline at end of file
+}