jackson-module-kotlin's incompatibility between 2.10.0 to 2.10.1 In Jackson 2.11.x+, there's jackson-module-kotlin's serialization result is incomptible. Reproducing method: Kotlin data class contains the field named /is.*/ Building project ./gradlew :jackson210:run :jackson211:run Result Jackson version: 2.10.0 {"usingBar":true} Jackson version: 2.10.1 {"isUsingBar":true} See also FasterXML/jackson-module-kotlin#80