diff --git a/codegen/src/main/kotlin/apifi/codegen/ApiBuilder.kt b/codegen/src/main/kotlin/apifi/codegen/ApiBuilder.kt
index eec9402..473c4b8 100644
--- a/codegen/src/main/kotlin/apifi/codegen/ApiBuilder.kt
+++ b/codegen/src/main/kotlin/apifi/codegen/ApiBuilder.kt
@@ -11,7 +11,7 @@ object ApiBuilder {
 
     private const val micronautHttpAnnotation = "io.micronaut.http.annotation"
 
-    fun build(name: String, paths: List<Path>, basePackageName: String, modelMapping: Map<String, String>): FileSpec {
+    fun build(name: String, paths: List<Path>, basePackageName: String, modelMapping: List<Pair<String, String>>): FileSpec {
         val baseName = toTitleCase(name)
         val controllerClassName = "${baseName}Api"
 
@@ -36,7 +36,7 @@ object ApiBuilder {
         return FileSpec.builder(basePackageName, "$controllerClassName.kt").addType(classSpec.build()).addType(controllerInterfaceClass).build()
     }
 
-    private fun generateOperationFunctions(paths: List<Path>, basePackageName: String, modelMapping: Map<String, String>): List<FunSpec> {
+    private fun generateOperationFunctions(paths: List<Path>, basePackageName: String, modelMapping: List<Pair<String, String>>): List<FunSpec> {
         return paths.flatMap { path ->
             path.operations?.map { operation ->
                 val serviceCallStatement = controllerCallStatement(operation, modelMapping)
diff --git a/codegen/src/main/kotlin/apifi/codegen/CodeGenerator.kt b/codegen/src/main/kotlin/apifi/codegen/CodeGenerator.kt
index 42f669b..ab88c1f 100644
--- a/codegen/src/main/kotlin/apifi/codegen/CodeGenerator.kt
+++ b/codegen/src/main/kotlin/apifi/codegen/CodeGenerator.kt
@@ -7,8 +7,8 @@ import com.squareup.kotlinpoet.TypeSpec
 
 object CodeGenerator {
     fun generate(spec: Spec, basePackageName: String): List<FileSpec> {
-        val modelFiles: List<FileSpec> = if (spec.models.isNotEmpty()) listOf(ModelFileBuilder.build(spec.models, basePackageName)) else emptyList()
-        val modelMapping = modelFiles.flatMap { it.members.mapNotNull { m -> (m as TypeSpec).name }.map { name -> name to "${it.packageName}.$name" } }.toMap()
+        val modelFiles: List<FileSpec> = if(spec.models.isNotEmpty()) listOf(ModelFileBuilder.build(spec.models, basePackageName)) else emptyList()
+        val modelMapping = modelFiles.flatMap { it.members.mapNotNull { m -> (m as TypeSpec).name }.map { name -> name to "${it.packageName}.$name" } }
 
         val apiGroups = spec.paths.groupBy { it.operations?.firstOrNull { o -> o.tags != null }?.tags?.firstOrNull() }.filter { it.key != null }
 
diff --git a/codegen/src/main/kotlin/apifi/codegen/ModelFileBuilder.kt b/codegen/src/main/kotlin/apifi/codegen/ModelFileBuilder.kt
index d5cb50b..ee097b0 100644
--- a/codegen/src/main/kotlin/apifi/codegen/ModelFileBuilder.kt
+++ b/codegen/src/main/kotlin/apifi/codegen/ModelFileBuilder.kt
@@ -7,7 +7,7 @@ import com.squareup.kotlinpoet.*
 object ModelFileBuilder {
     fun build(models: List<Model>, basePackageName: String): FileSpec {
         val packageName = "$basePackageName.models"
-        val baseModelMapping = models.map { it.name to "$packageName.${it.name}" }.toMap()
+        val baseModelMapping = models.map { it.name to "$packageName.${it.name}" }
         val builder = FileSpec.builder(packageName, "Models.kt")
         models.forEach { model ->
             builder.addType(
diff --git a/codegen/src/main/kotlin/apifi/codegen/RequestBodyBuilder.kt b/codegen/src/main/kotlin/apifi/codegen/RequestBodyBuilder.kt
index 245e0f3..496e77f 100644
--- a/codegen/src/main/kotlin/apifi/codegen/RequestBodyBuilder.kt
+++ b/codegen/src/main/kotlin/apifi/codegen/RequestBodyBuilder.kt
@@ -5,7 +5,7 @@ import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.ParameterSpec
 
 object RequestBodyBuilder {
-  fun build(bodyType: String, modelMapping: Map<String, String>): ParameterSpec =
+  fun build(bodyType: String, modelMapping: List<Pair<String, String>>): ParameterSpec =
       ParameterSpec.builder("body", bodyType.toKotlinPoetType(modelMapping))
           .addAnnotation(ClassName("io.micronaut.http.annotation", "Body"))
           .build()
diff --git a/codegen/src/main/kotlin/apifi/helpers/Functions.kt b/codegen/src/main/kotlin/apifi/helpers/Functions.kt
index 74023b5..449bda2 100644
--- a/codegen/src/main/kotlin/apifi/helpers/Functions.kt
+++ b/codegen/src/main/kotlin/apifi/helpers/Functions.kt
@@ -15,10 +15,10 @@ fun toCamelCase(s: String): String = CaseUtils.toCamelCase(s, false, '_', '-', '
 fun <T> Schema<T>.toCodeGenModel(name: String): CodegenModel = KotlinClientCodegen().fromModel(name, this, null)
 fun <T> Schema<T>.toCodeGenModel(): CodegenModel = this.toCodeGenModel("any")
 
-fun String.toKotlinPoetType(): TypeName = toKotlinPoetType(emptyMap())
+fun String.toKotlinPoetType(): TypeName = toKotlinPoetType(emptyList())
 
-fun String.toKotlinPoetType(packageNameMapping: Map<String, String>): TypeName {
-    val withPackage = { name: String -> ClassName.bestGuess(packageNameMapping[name] ?: name) }
+fun String.toKotlinPoetType(packageNameMapping: List<Pair<String, String>>): TypeName {
+    val withPackage = { name: String -> ClassName.bestGuess(packageNameMapping.find { name == it.first }?.second ?: name) }
     return if (this.contains("<")) {
         val parts = this.split('<')
         val primaryType = parts[0]
diff --git a/codegen/src/test/kotlin/apifi/codegen/ApiBuilderTest.kt b/codegen/src/test/kotlin/apifi/codegen/ApiBuilderTest.kt
index 9df51bb..09ca3e7 100644
--- a/codegen/src/test/kotlin/apifi/codegen/ApiBuilderTest.kt
+++ b/codegen/src/test/kotlin/apifi/codegen/ApiBuilderTest.kt
@@ -138,4 +138,4 @@ class ApiBuilderTest : DescribeSpec({
 
 })
 
-fun modelMapping() = mapOf("Pet" to "models.Pet", "PetResponse" to "models.PetResponse")
+fun modelMapping() = listOf("Pet" to "models.Pet", "PetResponse" to "models.PetResponse")
diff --git a/codegen/src/test/kotlin/apifi/codegen/RequestBodyBuilderTest.kt b/codegen/src/test/kotlin/apifi/codegen/RequestBodyBuilderTest.kt
index 39eb8c2..9e571cb 100644
--- a/codegen/src/test/kotlin/apifi/codegen/RequestBodyBuilderTest.kt
+++ b/codegen/src/test/kotlin/apifi/codegen/RequestBodyBuilderTest.kt
@@ -7,7 +7,7 @@ class RequestBodyBuilderTest : DescribeSpec( {
 
     describe("Request Body Builder") {
         it("should generate request body type") {
-            val requestBody = RequestBodyBuilder.build("Pet", mapOf("Pet" to "models.Pet"))
+            val requestBody = RequestBodyBuilder.build("Pet", listOf("Pet" to "models.Pet"))
             requestBody.toString() shouldBe "@io.micronaut.http.annotation.Body body: models.Pet"
         }
     }