diff --git a/springdoc-openapi-starter-common/src/main/java/org/springdoc/core/customizers/KotlinNullablePropertyCustomizer.kt b/springdoc-openapi-starter-common/src/main/java/org/springdoc/core/customizers/KotlinNullablePropertyCustomizer.kt
index 7c1b582b8..101410e0d 100644
--- a/springdoc-openapi-starter-common/src/main/java/org/springdoc/core/customizers/KotlinNullablePropertyCustomizer.kt
+++ b/springdoc-openapi-starter-common/src/main/java/org/springdoc/core/customizers/KotlinNullablePropertyCustomizer.kt
@@ -127,7 +127,7 @@ class KotlinNullablePropertyCustomizer(
 	/**
 	 * Marks a non-$ref property as nullable.
 	 * - OAS 3.0: `nullable: true`
-	 * - OAS 3.1: adds `"null"` to the `types` set
+	 * - OAS 3.1: adds `"null"` to the `types` set, or to `oneOf` for a composed schema
 	 *
 	 * A schema representing `Any?` carries no `type`/`types` constraint, i.e. it is an
 	 * "any" schema which already permits any value including `null`. Such a schema is left
@@ -138,9 +138,15 @@ class KotlinNullablePropertyCustomizer(
 		if (isAnySchema(property)) return
 
 		if (specVersion == SpecVersion.V31) {
-			val currentTypes = property.types ?: property.type?.let { setOf(it) } ?: emptySet()
-			if ("null" !in currentTypes) {
-				property.types = currentTypes + "null"
+			if (!property.oneOf.isNullOrEmpty()) {
+				if (property.oneOf.none { it.type == "null" || "null" in (it.types ?: emptySet()) }) {
+					property.oneOf = property.oneOf + Schema<Any>().apply { addType("null") }
+				}
+			} else {
+				val currentTypes = property.types ?: property.type?.let { setOf(it) } ?: emptySet()
+				if ("null" !in currentTypes) {
+					property.types = currentTypes + "null"
+				}
 			}
 		} else {
 			property.nullable = true
@@ -155,7 +161,8 @@ class KotlinNullablePropertyCustomizer(
 	private fun isAnySchema(property: Schema<*>): Boolean =
 		property.`$ref` == null &&
 			property.type == null &&
-			property.types.isNullOrEmpty()
+			property.types.isNullOrEmpty() &&
+			property.oneOf.isNullOrEmpty()
 
 	/**
 	 * Wraps a $ref property in a nullable composite schema. A fresh wrapper schema is returned
diff --git a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v30/app18/NullableController.kt b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v30/app18/NullableController.kt
index 88d11b2f0..836bf5e81 100644
--- a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v30/app18/NullableController.kt
+++ b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v30/app18/NullableController.kt
@@ -11,6 +11,7 @@ data class NullableFieldsResponse(
 	val nullableAny: Any? = null,
 	@field:Schema(description = "The nested object")
 	val nullableNested: NestedObject? = null,
+	val nullableComposed: ComposedObject? = null,
 )
 
 data class NestedObject(
@@ -18,6 +19,12 @@ data class NestedObject(
 	val description: String? = null,
 )
 
+sealed class ComposedObject {
+	data class First(val first: String) : ComposedObject()
+
+	data class Second(val second: String) : ComposedObject()
+}
+
 @RestController
 class NullableController {
 	@GetMapping("/nullable")
diff --git a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v31/app23/NullableController.kt b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v31/app23/NullableController.kt
index 8caecbdc3..f3d861cd5 100644
--- a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v31/app23/NullableController.kt
+++ b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v31/app23/NullableController.kt
@@ -11,6 +11,7 @@ data class NullableFieldsResponse(
 	val nullableAny: Any? = null,
 	@field:Schema(description = "The nested object")
 	val nullableNested: NestedObject? = null,
+	val nullableComposed: ComposedObject? = null,
 )
 
 data class NestedObject(
@@ -18,6 +19,12 @@ data class NestedObject(
 	val description: String? = null,
 )
 
+sealed class ComposedObject {
+	data class First(val first: String) : ComposedObject()
+
+	data class Second(val second: String) : ComposedObject()
+}
+
 @RestController
 class NullableController {
 	@GetMapping("/nullable")
diff --git a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.0.1/app18.json b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.0.1/app18.json
index cbcb8e772..0c80bbc6a 100644
--- a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.0.1/app18.json
+++ b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.0.1/app18.json
@@ -34,6 +34,28 @@
   },
   "components": {
     "schemas": {
+      "ComposedObject": {
+        "type": "object"
+      },
+      "First": {
+        "required": [
+          "first"
+        ],
+        "type": "object",
+        "allOf": [
+          {
+            "$ref": "#/components/schemas/ComposedObject"
+          },
+          {
+            "type": "object",
+            "properties": {
+              "first": {
+                "type": "string"
+              }
+            }
+          }
+        ]
+      },
       "NestedObject": {
         "required": [
           "name"
@@ -79,8 +101,38 @@
                 "$ref": "#/components/schemas/NestedObject"
               }
             ]
+          },
+          "nullableComposed": {
+            "nullable": true,
+            "oneOf": [
+              {
+                "$ref": "#/components/schemas/First"
+              },
+              {
+                "$ref": "#/components/schemas/Second"
+              }
+            ]
           }
         }
+      },
+      "Second": {
+        "required": [
+          "second"
+        ],
+        "type": "object",
+        "allOf": [
+          {
+            "$ref": "#/components/schemas/ComposedObject"
+          },
+          {
+            "type": "object",
+            "properties": {
+              "second": {
+                "type": "string"
+              }
+            }
+          }
+        ]
       }
     }
   }
diff --git a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.1.0/app23.json b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.1.0/app23.json
index f25a1d44f..f1432afd3 100644
--- a/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.1.0/app23.json
+++ b/springdoc-openapi-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.1.0/app23.json
@@ -34,6 +34,25 @@
   },
   "components": {
     "schemas": {
+      "ComposedObject": { },
+      "First": {
+        "allOf": [
+          {
+            "$ref": "#/components/schemas/ComposedObject"
+          },
+          {
+            "type": "object",
+            "properties": {
+              "first": {
+                "type": "string"
+              }
+            }
+          }
+        ],
+        "required": [
+          "first"
+        ]
+      },
       "NestedObject": {
         "type": "object",
         "properties": {
@@ -81,11 +100,42 @@
                 "type": "null"
               }
             ]
+          },
+          "nullableComposed": {
+            "oneOf": [
+              {
+                "$ref": "#/components/schemas/First"
+              },
+              {
+                "$ref": "#/components/schemas/Second"
+              },
+              {
+                "type": "null"
+              }
+            ]
           }
         },
         "required": [
           "requiredField"
         ]
+      },
+      "Second": {
+        "allOf": [
+          {
+            "$ref": "#/components/schemas/ComposedObject"
+          },
+          {
+            "type": "object",
+            "properties": {
+              "second": {
+                "type": "string"
+              }
+            }
+          }
+        ],
+        "required": [
+          "second"
+        ]
       }
     }
   }