diff --git a/src/main/kotlin/dev/usbharu/hideout/Application.kt b/src/main/kotlin/dev/usbharu/hideout/Application.kt
index 0d33b97d..6952fe31 100644
--- a/src/main/kotlin/dev/usbharu/hideout/Application.kt
+++ b/src/main/kotlin/dev/usbharu/hideout/Application.kt
@@ -22,6 +22,7 @@ import io.ktor.serialization.jackson.*
 import io.ktor.server.application.*
 import org.jetbrains.exposed.sql.Database
 import org.koin.ktor.ext.inject
+import java.lang.Compiler.enable
 import java.util.*
 
 fun main(args: Array<String>): Unit = io.ktor.server.netty.EngineMain.main(args)
@@ -49,7 +50,7 @@ fun Application.module() {
             HttpClient(CIO) {
                 install(ContentNegotiation) {
 
-                    jackson(ContentType.Application.Activity) {
+                    jackson {
                         enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
                         setSerializationInclusion(JsonInclude.Include.NON_EMPTY)
                         configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
diff --git a/src/main/kotlin/dev/usbharu/hideout/service/ActivityPubUserService.kt b/src/main/kotlin/dev/usbharu/hideout/service/ActivityPubUserService.kt
index b870c6dc..d4f9d18c 100644
--- a/src/main/kotlin/dev/usbharu/hideout/service/ActivityPubUserService.kt
+++ b/src/main/kotlin/dev/usbharu/hideout/service/ActivityPubUserService.kt
@@ -2,6 +2,7 @@ package dev.usbharu.hideout.service
 
 import dev.usbharu.hideout.ap.*
 import dev.usbharu.hideout.config.Config
+import dev.usbharu.hideout.util.HttpUtil.Activity
 import io.ktor.client.*
 import io.ktor.client.call.*
 import io.ktor.client.plugins.*
@@ -48,6 +49,7 @@ class ActivityPubUserService(
         val person = webFingerService.fetchUserModel(actor) ?: throw IllegalArgumentException("actor is not found")
         val inboxUrl = person.inbox ?: throw IllegalArgumentException("inbox is not found")
         httpClient.post(inboxUrl) {
+            contentType(ContentType.Application.Activity)
             setBody(Accept(
                     name = "Follow",
                     `object` = follow,