diff --git a/zio-http/jvm/src/test/scala/zio/http/endpoint/openapi/OpenAPIGenSpec.scala b/zio-http/jvm/src/test/scala/zio/http/endpoint/openapi/OpenAPIGenSpec.scala
index 967bd1630d5..efe02f838f9 100644
--- a/zio-http/jvm/src/test/scala/zio/http/endpoint/openapi/OpenAPIGenSpec.scala
+++ b/zio-http/jvm/src/test/scala/zio/http/endpoint/openapi/OpenAPIGenSpec.scala
@@ -160,6 +160,11 @@ object OpenAPIGenSpec extends ZIOSpecDefault {
     implicit def schema[T: Schema]: Schema[WithGenericPayload[T]] = DeriveSchema.gen
   }
 
+  final case class WithOptionalAdtPayload(optionalAdtField: Option[SealedTraitCustomDiscriminator])
+  object WithOptionalAdtPayload {
+    implicit val schema: Schema[WithOptionalAdtPayload] = DeriveSchema.gen
+  }
+
   private val simpleEndpoint =
     Endpoint(
       (GET / "static" / int("id") / uuid("uuid") ?? Doc.p("user id") / string("name")) ?? Doc.p("get path"),
@@ -2231,9 +2236,9 @@ object OpenAPIGenSpec extends ZIOSpecDefault {
             |        "discriminator" : {
             |          "propertyName" : "type",
             |          "mapping" : {
-            |            "One" : "#/components/schemas/One}",
-            |            "Two" : "#/components/schemas/Two}",
-            |            "three" : "#/components/schemas/Three}"
+            |            "One" : "#/components/schemas/One",
+            |            "Two" : "#/components/schemas/Two",
+            |            "three" : "#/components/schemas/Three"
             |          }
             |        }
             |      },
@@ -2810,7 +2815,10 @@ object OpenAPIGenSpec extends ZIOSpecDefault {
             |            ]
             |          },
             |          "nestedOption" : {
-            |            "$ref" : "#/components/schemas/Recursive"
+            |            "anyOf" : [
+            |              { "type" : "null" },
+            |              { "$ref" : "#/components/schemas/Recursive" }
+            |            ]
             |          },
             |          "nestedMap" : {
             |            "type" : "object",
@@ -2989,6 +2997,114 @@ object OpenAPIGenSpec extends ZIOSpecDefault {
                              |""".stripMargin
         assertTrue(json == toJsonAst(expectedJson))
       },
+      test("Optional ADT payload") {
+        val endpoint     = Endpoint(GET / "static").in[WithOptionalAdtPayload]
+        val generated    = OpenAPIGen.fromEndpoints("Simple Endpoint", "1.0", endpoint)
+        val json         = toJsonAst(generated)
+        val expectedJson =
+          """{
+            |  "openapi" : "3.1.0",
+            |  "info" : {
+            |    "title" : "Simple Endpoint",
+            |    "version" : "1.0"
+            |  },
+            |  "paths" : {
+            |    "/static" : {
+            |      "get" : {
+            |        "requestBody" :
+            |          {
+            |          "content" : {
+            |            "application/json" : {
+            |              "schema" :
+            |                {
+            |                "$ref" : "#/components/schemas/WithOptionalAdtPayload"
+            |              }
+            |            }
+            |          },
+            |          "required" : true
+            |        }
+            |      }
+            |    }
+            |  },
+            |  "components" : {
+            |    "schemas" : {
+            |      "One" :
+            |        {
+            |        "type" :
+            |          "object",
+            |        "properties" : {}
+            |      },
+            |      "SealedTraitCustomDiscriminator" :
+            |        {
+            |        "oneOf" : [
+            |          {
+            |            "$ref" : "#/components/schemas/One"
+            |          },
+            |          {
+            |            "$ref" : "#/components/schemas/Two"
+            |          },
+            |          {
+            |            "$ref" : "#/components/schemas/Three"
+            |          }
+            |        ],
+            |        "discriminator" : {
+            |          "propertyName" : "type",
+            |          "mapping" : {
+            |            "One" : "#/components/schemas/One",
+            |            "Two" : "#/components/schemas/Two",
+            |            "three" : "#/components/schemas/Three"
+            |          }
+            |        }
+            |      },
+            |      "WithOptionalAdtPayload" :
+            |        {
+            |        "type" :
+            |          "object",
+            |        "properties" : {
+            |          "optionalAdtField" : {
+            |            "anyOf": [
+            |              { "type": "null" },
+            |              { "$ref": "#/components/schemas/SealedTraitCustomDiscriminator" }
+            |            ]
+            |          }
+            |        },
+            |        "required" : [
+            |          "optionalAdtField"
+            |        ]
+            |      },
+            |      "Two" :
+            |        {
+            |        "type" :
+            |          "object",
+            |        "properties" : {
+            |          "name" : {
+            |            "type" :
+            |              "string"
+            |          }
+            |        },
+            |        "required" : [
+            |          "name"
+            |        ]
+            |      },
+            |      "Three" :
+            |        {
+            |        "type" :
+            |          "object",
+            |        "properties" : {
+            |          "name" : {
+            |            "type" :
+            |              "string"
+            |          }
+            |        },
+            |        "required" : [
+            |          "name"
+            |        ]
+            |      }
+            |    }
+            |  }
+            |}""".stripMargin
+        assertTrue(json == toJsonAst(expectedJson))
+      },
     )
 
 }
diff --git a/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/JsonSchema.scala b/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/JsonSchema.scala
index ed8e1bc2847..8e4668435a8 100644
--- a/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/JsonSchema.scala
+++ b/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/JsonSchema.scala
@@ -12,7 +12,7 @@ import zio.schema.codec._
 import zio.schema.codec.json._
 import zio.schema.validation._
 
-import zio.http.codec.{PathCodec, SegmentCodec, TextCodec}
+import zio.http.codec.{SegmentCodec, TextCodec}
 
 @nowarn("msg=possible missing interpolator")
 private[openapi] case class SerializableJsonSchema(
@@ -47,23 +47,35 @@ private[openapi] case class SerializableJsonSchema(
   uniqueItems: Option[Boolean] = None,
   minItems: Option[Int] = None,
 ) {
-  def asNullableType(nullable: Boolean): SerializableJsonSchema =
+  def asNullableType(nullable: Boolean): SerializableJsonSchema = {
+    import SerializableJsonSchema.typeNull
+
     if (nullable && schemaType.isDefined)
       copy(schemaType = Some(schemaType.get.add("null")))
     else if (nullable && oneOf.isDefined)
-      copy(oneOf = Some(oneOf.get :+ SerializableJsonSchema(schemaType = Some(TypeOrTypes.Type("null")))))
+      copy(oneOf = Some(oneOf.get :+ typeNull))
     else if (nullable && allOf.isDefined)
-      SerializableJsonSchema(allOf =
-        Some(Chunk(this, SerializableJsonSchema(schemaType = Some(TypeOrTypes.Type("null"))))),
-      )
+      SerializableJsonSchema(allOf = Some(Chunk(this, typeNull)))
     else if (nullable && anyOf.isDefined)
-      copy(anyOf = Some(anyOf.get :+ SerializableJsonSchema(schemaType = Some(TypeOrTypes.Type("null")))))
+      copy(anyOf = Some(anyOf.get :+ typeNull))
+    else if (nullable && ref.isDefined && default.isEmpty)
+      SerializableJsonSchema(anyOf = Some(Chunk(typeNull, this)))
     else
       this
-
+  }
 }
 
 private[openapi] object SerializableJsonSchema {
+
+  /**
+   * Used to generate a OpenAPI schema part looking like this:
+   * {{{
+   *   { "type": "null"}
+   * }}}
+   */
+  private[SerializableJsonSchema] val typeNull: SerializableJsonSchema =
+    SerializableJsonSchema(schemaType = Some(TypeOrTypes.Type("null")))
+
   implicit val doubleOrLongSchema: Schema[Either[Double, Long]] =
     Schema.fallback(Schema[Double], Schema[Long]).transform(_.toEither, Fallback.fromEither)
 
@@ -766,7 +778,8 @@ object JsonSchema {
       case nominal: TypeId.Nominal if referenceType == SchemaStyle.Reference =>
         Some(s"#/components/schemas/${nominal.fullyQualified.replace(".", "_")}")
       case nominal: TypeId.Nominal if referenceType == SchemaStyle.Compact   =>
-        Some(s"#/components/schemas/${nominal.typeName}")
+        val toto = s"#/components/schemas/${nominal.typeName}"
+        Some(toto)
       case _                                                                 =>
         None
     }
diff --git a/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/OpenAPIGen.scala b/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/OpenAPIGen.scala
index 2e4d0e500f4..dee8fe54764 100644
--- a/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/OpenAPIGen.scala
+++ b/zio-http/shared/src/main/scala/zio/http/endpoint/openapi/OpenAPIGen.scala
@@ -988,7 +988,7 @@ object OpenAPIGen {
   }
   private def schemaReferencePath(nominal: TypeId.Nominal, referenceType: SchemaStyle): String = {
     referenceType match {
-      case SchemaStyle.Compact => s"#/components/schemas/${nominal.typeName}}"
+      case SchemaStyle.Compact => s"#/components/schemas/${nominal.typeName}"
       case _                   => s"#/components/schemas/${nominal.fullyQualified.replace(".", "_")}}"
     }
   }