diff --git a/buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java b/buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java
index cdf7708ca4..6d2a5a13da 100644
--- a/buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java
+++ b/buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java
@@ -49,8 +49,8 @@ class KotlinConventions {
 
 	private void configure(KotlinCompile compile) {
 		KotlinJvmOptions kotlinOptions = compile.getKotlinOptions();
-		kotlinOptions.setApiVersion("1.6");
-		kotlinOptions.setLanguageVersion("1.6");
+		kotlinOptions.setApiVersion("1.3");
+		kotlinOptions.setLanguageVersion("1.3");
 		kotlinOptions.setJvmTarget("1.8");
 		kotlinOptions.setAllWarningsAsErrors(true);
 		List<String> freeCompilerArgs = new ArrayList<>(compile.getKotlinOptions().getFreeCompilerArgs());
diff --git a/spring-boot-project/spring-boot-docs/build.gradle b/spring-boot-project/spring-boot-docs/build.gradle
index 71a7c9563e..2a23cb8301 100644
--- a/spring-boot-project/spring-boot-docs/build.gradle
+++ b/spring-boot-project/spring-boot-docs/build.gradle
@@ -40,6 +40,11 @@ plugins.withType(EclipsePlugin) {
 	}
 }
 
+tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile) { 
+	kotlinOptions.apiVersion = '1.6'
+	kotlinOptions.languageVersion = '1.6'
+}
+
 dependencies {
 	actuatorApiDocumentation(project(path: ":spring-boot-project:spring-boot-actuator-autoconfigure", configuration: "documentation"))