diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/infrastructure/ApiClient.kt.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/infrastructure/ApiClient.kt.mustache
index de3db091a8fd..8f3d31ad09a8 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/infrastructure/ApiClient.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/infrastructure/ApiClient.kt.mustache
@@ -12,6 +12,7 @@ import io.ktor.client.request.parameter
 import io.ktor.client.request.request
 import io.ktor.client.request.setBody
 import io.ktor.client.statement.HttpResponse
+import io.ktor.http.ContentType
 import io.ktor.http.contentType
 import io.ktor.http.HttpHeaders
 import io.ktor.http.HttpMethod
@@ -196,6 +197,7 @@ import {{packageName}}.auth.*
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
             if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+                contentType(ContentType.Application.Json)
                 setBody(body)
             }
         }
diff --git a/samples/client/petstore/kotlin-jvm-ktor-gson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-jvm-ktor-gson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
index 6e9f06023343..832d78f75809 100644
--- a/samples/client/petstore/kotlin-jvm-ktor-gson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-jvm-ktor-gson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -12,6 +12,7 @@ import io.ktor.client.request.parameter
 import io.ktor.client.request.request
 import io.ktor.client.request.setBody
 import io.ktor.client.statement.HttpResponse
+import io.ktor.http.ContentType
 import io.ktor.http.contentType
 import io.ktor.http.HttpHeaders
 import io.ktor.http.HttpMethod
@@ -156,6 +157,7 @@ open class ApiClient(
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
             if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+                contentType(ContentType.Application.Json)
                 setBody(body)
             }
         }
diff --git a/samples/client/petstore/kotlin-jvm-ktor-jackson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-jvm-ktor-jackson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
index 69fcc0ab8547..180e34f6ee7c 100644
--- a/samples/client/petstore/kotlin-jvm-ktor-jackson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-jvm-ktor-jackson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -12,6 +12,7 @@ import io.ktor.client.request.parameter
 import io.ktor.client.request.request
 import io.ktor.client.request.setBody
 import io.ktor.client.statement.HttpResponse
+import io.ktor.http.ContentType
 import io.ktor.http.contentType
 import io.ktor.http.HttpHeaders
 import io.ktor.http.HttpMethod
@@ -164,6 +165,7 @@ open class ApiClient(
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
             if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+                contentType(ContentType.Application.Json)
                 setBody(body)
             }
         }
diff --git a/samples/client/petstore/kotlin-jvm-ktor-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-jvm-ktor-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
index 762dad7221a4..be26af2d0c43 100644
--- a/samples/client/petstore/kotlin-jvm-ktor-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-jvm-ktor-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -12,6 +12,7 @@ import io.ktor.client.request.parameter
 import io.ktor.client.request.request
 import io.ktor.client.request.setBody
 import io.ktor.client.statement.HttpResponse
+import io.ktor.http.ContentType
 import io.ktor.http.contentType
 import io.ktor.http.HttpHeaders
 import io.ktor.http.HttpMethod
@@ -147,6 +148,7 @@ open class ApiClient(
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
             if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+                contentType(ContentType.Application.Json)
                 setBody(body)
             }
         }