diff --git a/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedClassTest.kt b/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedClassTest.kt
index efa39cab2..631532156 100644
--- a/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedClassTest.kt
+++ b/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedClassTest.kt
@@ -2,6 +2,8 @@ package io.mockk.it
 
 import io.mockk.every
 import io.mockk.mockk
+import org.junit.jupiter.api.condition.DisabledForJreRange
+import org.junit.jupiter.api.condition.JRE
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -30,6 +32,18 @@ class SealedClassTest {
         assertEquals(Leaf(1), result)
     }
 
+    @Test
+    fun serviceTakesSealedClassAsInput() {
+        val formattedNode = "Formatted node"
+        val factory = mockk<Factory> {
+            every { format(any()) } answers { formattedNode }
+        }
+
+        val result = factory.format(Root(0))
+
+        assertEquals(formattedNode, result)
+    }
+
     companion object {
 
         sealed class Node
@@ -39,10 +53,14 @@ class SealedClassTest {
 
         interface Factory {
             fun create(): Node
+
+            fun format(node: Node): String
         }
 
         class FactoryImpl : Factory {
             override fun create(): Node = Root(0)
+
+            override fun format(node: Node): String = node.toString()
         }
 
     }
diff --git a/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedInterfaceTest.kt b/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedInterfaceTest.kt
index 91f727abf..5001fe6aa 100644
--- a/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedInterfaceTest.kt
+++ b/modules/mockk/src/commonTest/kotlin/io/mockk/it/SealedInterfaceTest.kt
@@ -2,6 +2,8 @@ package io.mockk.it
 
 import io.mockk.every
 import io.mockk.mockk
+import org.junit.jupiter.api.condition.DisabledForJreRange
+import org.junit.jupiter.api.condition.JRE
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -30,6 +32,18 @@ class SealedInterfaceTest {
         assertEquals(Leaf(1), result)
     }
 
+    @Test
+    fun serviceTakesSealedInterfaceAsInput() {
+        val formattedNode = "Formatted node"
+        val factory = mockk<Factory> {
+            every { format(any()) } answers { formattedNode }
+        }
+
+        val result = factory.format(Root(0))
+
+        assertEquals(formattedNode, result)
+    }
+
     companion object {
 
         sealed interface Node
@@ -39,10 +53,14 @@ class SealedInterfaceTest {
 
         interface Factory {
             fun create(): Node
+
+            fun format(node: Node): String
         }
 
         class FactoryImpl : Factory {
             override fun create(): Node = Root(0)
+
+            override fun format(node: Node): String = node.toString()
         }
 
     }
diff --git a/modules/mockk/src/jvmMain/kotlin/io/mockk/impl/recording/JvmSignatureValueGenerator.kt b/modules/mockk/src/jvmMain/kotlin/io/mockk/impl/recording/JvmSignatureValueGenerator.kt
index 20a0278e2..e70e4e6b8 100644
--- a/modules/mockk/src/jvmMain/kotlin/io/mockk/impl/recording/JvmSignatureValueGenerator.kt
+++ b/modules/mockk/src/jvmMain/kotlin/io/mockk/impl/recording/JvmSignatureValueGenerator.kt
@@ -24,24 +24,34 @@ class JvmSignatureValueGenerator(val rnd: Random) : SignatureValueGenerator {
             return constructor.call(valueSig)
         }
 
-        return cls.cast(
-            when (cls) {
-                java.lang.Boolean::class -> rnd.nextBoolean()
-                java.lang.Byte::class -> rnd.nextInt().toByte()
-                java.lang.Short::class -> rnd.nextInt().toShort()
-                java.lang.Character::class -> rnd.nextInt().toChar()
-                java.lang.Integer::class -> rnd.nextInt()
-                java.lang.Long::class -> rnd.nextLong()
-                java.lang.Float::class -> rnd.nextFloat()
-                java.lang.Double::class -> rnd.nextDouble()
-                java.lang.String::class -> rnd.nextLong().toString(16)
+        return cls.cast(instantiate(cls, anyValueGeneratorProvider, instantiator))
+    }
+
+    private fun <T : Any> instantiate(
+        cls: KClass<T>,
+        anyValueGeneratorProvider: () -> AnyValueGenerator,
+        instantiator: AbstractInstantiator
+    ): Any = when (cls) {
+        Boolean::class -> rnd.nextBoolean()
+        Byte::class -> rnd.nextInt().toByte()
+        Short::class -> rnd.nextInt().toShort()
+        Character::class -> rnd.nextInt().toChar()
+        Integer::class -> rnd.nextInt()
+        Long::class -> rnd.nextLong()
+        Float::class -> rnd.nextFloat()
+        Double::class -> rnd.nextDouble()
+        String::class -> rnd.nextLong().toString(16)
 
-                else ->
-                    @Suppress("UNCHECKED_CAST")
-                    anyValueGeneratorProvider().anyValue(cls, isNullable = false) {
-                        instantiator.instantiate(cls)
-                    } as T
+        else ->
+            if (cls.isSealed) {
+                cls.sealedSubclasses.firstNotNullOfOrNull {
+                    instantiate(it, anyValueGeneratorProvider, instantiator)
+                } ?: error("Unable to create proxy for sealed class $cls, available subclasses: ${cls.sealedSubclasses}")
+            } else {
+                @Suppress("UNCHECKED_CAST")
+                anyValueGeneratorProvider().anyValue(cls, isNullable = false) {
+                    instantiator.instantiate(cls)
+                } as T
             }
-        )
     }
 }