diff --git a/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/AwsServiceConfigIntegration.kt b/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/AwsServiceConfigIntegration.kt
index ca4e1251700..9b4a7f81fda 100644
--- a/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/AwsServiceConfigIntegration.kt
+++ b/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/AwsServiceConfigIntegration.kt
@@ -9,8 +9,8 @@ import software.amazon.smithy.kotlin.codegen.integration.KotlinIntegration
 import software.amazon.smithy.kotlin.codegen.integration.SectionWriterBinding
 import software.amazon.smithy.kotlin.codegen.lang.KotlinTypes
 import software.amazon.smithy.kotlin.codegen.model.asNullable
-import software.amazon.smithy.kotlin.codegen.model.boxed
 import software.amazon.smithy.kotlin.codegen.model.knowledge.AwsSignatureVersion4
+import software.amazon.smithy.kotlin.codegen.model.nullable
 import software.amazon.smithy.kotlin.codegen.rendering.*
 import software.amazon.smithy.kotlin.codegen.rendering.util.ConfigProperty
 import software.amazon.smithy.kotlin.codegen.rendering.util.ConfigPropertyType
@@ -22,7 +22,7 @@ class AwsServiceConfigIntegration : KotlinIntegration {
     companion object {
         val RegionProp: ConfigProperty = ConfigProperty {
             name = "region"
-            symbol = KotlinTypes.String.toBuilder().boxed().build()
+            symbol = KotlinTypes.String.toBuilder().nullable().build()
             baseClass = AwsRuntimeTypes.Core.Client.AwsSdkClientConfig
             useNestedBuilderBaseClass()
             documentation = """
diff --git a/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/eventstream/EventStreamParserGenerator.kt b/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/eventstream/EventStreamParserGenerator.kt
index 142da61844a..45f86311712 100644
--- a/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/eventstream/EventStreamParserGenerator.kt
+++ b/codegen/smithy-aws-kotlin-codegen/src/main/kotlin/aws/sdk/kotlin/codegen/protocols/eventstream/EventStreamParserGenerator.kt
@@ -137,7 +137,7 @@ class EventStreamParserGenerator(
                     else -> throw CodegenException("unsupported eventHeader shape: member=$hdrBinding; targetShape=$target")
                 }
 
-                val defaultValuePostfix = if (targetSymbol.isNotBoxed && targetSymbol.defaultValue() != null) {
+                val defaultValuePostfix = if (targetSymbol.isNotNullable && targetSymbol.defaultValue() != null) {
                     " ?: ${targetSymbol.defaultValue()}"
                 } else {
                     ""
diff --git a/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/BoxServicesTest.kt b/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/BoxServicesTest.kt
index d465e68b2c4..43a1b1898c3 100644
--- a/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/BoxServicesTest.kt
+++ b/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/BoxServicesTest.kt
@@ -40,7 +40,7 @@ class BoxServicesTest {
             structure Other {}
             
             integer NotBoxedField
-        """.prependNamespaceAndService(operations = listOf("Foo")).toSmithyModel()
+        """.prependNamespaceAndService(version = "1", operations = listOf("Foo")).toSmithyModel()
 
         val ctx = model.newTestContext()
         val transformed = BoxServices().preprocessModel(model, ctx.generationCtx.settings)
diff --git a/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/RemoveEventStreamOperationsTest.kt b/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/RemoveEventStreamOperationsTest.kt
index 9dc1a78bf9c..fb0926788ef 100644
--- a/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/RemoveEventStreamOperationsTest.kt
+++ b/codegen/smithy-aws-kotlin-codegen/src/test/kotlin/aws/sdk/kotlin/codegen/customization/RemoveEventStreamOperationsTest.kt
@@ -23,6 +23,7 @@ class RemoveEventStreamOperationsTest {
             input: BlobInput
         }
         structure BlobInput {
+            @required
             blob: StreamingBlob
         }
         @streaming