diff --git a/release-notes/CREDITS-2.x b/release-notes/CREDITS-2.x
index 6fe440f2..309b593f 100644
--- a/release-notes/CREDITS-2.x
+++ b/release-notes/CREDITS-2.x
@@ -21,6 +21,7 @@ Stefan Schmid (schmist@github)
 wrongwrong (k163377@github)
 * #456: Refactor KNAI.findImplicitPropertyName()
 * #449: Refactor AnnotatedMethod.hasRequiredMarker()
+* #521: Fixed lookup of instantiators
 
 Dmitri Domanine (novtor@github)
 * Contributed fix for #490: Missing value of type JsonNode? is deserialized as NullNode instead of null
diff --git a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinValueInstantiator.kt b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinValueInstantiator.kt
index 2196d968..519b31ab 100644
--- a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinValueInstantiator.kt
+++ b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinValueInstantiator.kt
@@ -201,8 +201,15 @@ internal class KotlinInstantiators(
         defaultInstantiator: ValueInstantiator
     ): ValueInstantiator {
         return if (beanDescriptor.beanClass.isKotlinClass()) {
-            if (defaultInstantiator is StdValueInstantiator) {
-                KotlinValueInstantiator(defaultInstantiator, cache, nullToEmptyCollection, nullToEmptyMap, nullIsSameAsDefault, strictNullChecks)
+            if (defaultInstantiator::class == StdValueInstantiator::class) {
+                KotlinValueInstantiator(
+                    defaultInstantiator as StdValueInstantiator,
+                    cache,
+                    nullToEmptyCollection,
+                    nullToEmptyMap,
+                    nullIsSameAsDefault,
+                    strictNullChecks
+                )
             } else {
                 // TODO: return defaultInstantiator and let default method parameters and nullability go unused?  or die with exception:
                 throw IllegalStateException("KotlinValueInstantiator requires that the default ValueInstantiator is StdValueInstantiator")
diff --git a/src/test/kotlin/com/fasterxml/jackson/module/kotlin/KotlinInstantiatorsTest.kt b/src/test/kotlin/com/fasterxml/jackson/module/kotlin/KotlinInstantiatorsTest.kt
new file mode 100644
index 00000000..dad0fc60
--- /dev/null
+++ b/src/test/kotlin/com/fasterxml/jackson/module/kotlin/KotlinInstantiatorsTest.kt
@@ -0,0 +1,65 @@
+package com.fasterxml.jackson.module.kotlin
+
+import com.fasterxml.jackson.databind.deser.std.StdValueInstantiator
+import org.junit.Assert.*
+import org.junit.Test
+
+class KotlinInstantiatorsTest {
+    private val mapper = jacksonObjectMapper()
+    private val deserConfig = mapper.deserializationConfig
+
+    private val kotlinInstantiators = KotlinInstantiators(
+        ReflectionCache(10),
+        nullToEmptyCollection = false,
+        nullToEmptyMap = false,
+        nullIsSameAsDefault = false,
+        strictNullChecks = false
+    )
+
+    @Test
+    fun `Provides default instantiator for Java class`() {
+        val javaType = mapper.constructType(String::class.java)
+        val defaultInstantiator = StdValueInstantiator(deserConfig, javaType)
+        val instantiator = kotlinInstantiators.findValueInstantiator(
+            deserConfig,
+            deserConfig.introspect(javaType),
+            defaultInstantiator
+        )
+
+        assertEquals(defaultInstantiator, instantiator)
+    }
+
+    @Test
+    fun `Provides KotlinValueInstantiator for Kotlin class`() {
+        class TestClass
+
+        val javaType = mapper.constructType(TestClass::class.java)
+        val instantiator = kotlinInstantiators.findValueInstantiator(
+            deserConfig,
+            deserConfig.introspect(javaType),
+            StdValueInstantiator(deserConfig, javaType)
+        )
+
+        assertTrue(instantiator is StdValueInstantiator)
+        assertTrue(instantiator::class == KotlinValueInstantiator::class)
+    }
+
+    @Test
+    fun `Throws for Kotlin class when default instantiator isn't StdValueInstantiator`() {
+        class TestClass
+        class DefaultClass
+
+        val subClassInstantiator = object : StdValueInstantiator(
+            deserConfig,
+            mapper.constructType(DefaultClass::class.java)
+        ) {}
+
+        assertThrows(IllegalStateException::class.java) {
+            kotlinInstantiators.findValueInstantiator(
+                deserConfig,
+                deserConfig.introspect(mapper.constructType(TestClass::class.java)),
+                subClassInstantiator
+            )
+        }
+    }
+}
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