diff --git a/src/framework/types.ts b/src/framework/types.ts
index 41733a9c..57601da0 100644
--- a/src/framework/types.ts
+++ b/src/framework/types.ts
@@ -262,19 +262,29 @@ export namespace OpenAPIV3 {
     | 'string'
     | 'integer';
   export type ArraySchemaObjectType = 'array';
-  export type SchemaObject = ArraySchemaObject | NonArraySchemaObject;
 
-  export interface ArraySchemaObject extends BaseSchemaObject {
-    type: ArraySchemaObjectType;
+  export type SchemaObject = ArraySchemaObject | NonArraySchemaObject | CompositionSchemaObject;
+
+  export interface ArraySchemaObject extends BaseSchemaObject<ArraySchemaObjectType> {
     items: ReferenceObject | SchemaObject;
   }
 
-  export interface NonArraySchemaObject extends BaseSchemaObject {
-    type: NonArraySchemaObjectType;
+  export interface NonArraySchemaObject extends BaseSchemaObject<NonArraySchemaObjectType> {
   }
 
-  interface BaseSchemaObject {
+  export interface CompositionSchemaObject extends BaseSchemaObject<undefined> {
     // JSON schema allowed properties, adjusted for OpenAPI
+    allOf?: Array<ReferenceObject | SchemaObject>;
+    oneOf?: Array<ReferenceObject | SchemaObject>;
+    anyOf?: Array<ReferenceObject | SchemaObject>;
+    not?: ReferenceObject | SchemaObject;
+    // OpenAPI-specific properties
+    discriminator?: DiscriminatorObject;
+  }
+
+  interface BaseSchemaObject<T> {
+    // JSON schema allowed properties, adjusted for OpenAPI
+    type?: T;
     title?: string;
     description?: string;
     format?: string;
@@ -298,14 +308,9 @@ export namespace OpenAPIV3 {
     properties?: {
       [name: string]: ReferenceObject | SchemaObject;
     };
-    allOf?: Array<ReferenceObject | SchemaObject>;
-    oneOf?: Array<ReferenceObject | SchemaObject>;
-    anyOf?: Array<ReferenceObject | SchemaObject>;
-    not?: ReferenceObject | SchemaObject;
 
     // OpenAPI-specific properties
     nullable?: boolean;
-    discriminator?: DiscriminatorObject;
     readOnly?: boolean;
     writeOnly?: boolean;
     xml?: XMLObject;
diff --git a/src/middlewares/parsers/req.parameter.mutator.ts b/src/middlewares/parsers/req.parameter.mutator.ts
index de8bb69f..00ece3cd 100644
--- a/src/middlewares/parsers/req.parameter.mutator.ts
+++ b/src/middlewares/parsers/req.parameter.mutator.ts
@@ -183,7 +183,7 @@ export class RequestParameterMutator {
   ): void {
     // fetch the keys used for this kind of explode
     const type = schema.type;
-    const hasXOf = schema.allOf || schema.oneOf || schema.anyOf;
+    const hasXOf = schema['allOf'] || schema['oneOf'] || schema['anyOf'];
     const properties = hasXOf
       ? xOfProperties(schema)
       : type === 'object'
diff --git a/src/middlewares/parsers/schema.preprocessor.ts b/src/middlewares/parsers/schema.preprocessor.ts
index 3cd0396c..098cfcac 100644
--- a/src/middlewares/parsers/schema.preprocessor.ts
+++ b/src/middlewares/parsers/schema.preprocessor.ts
@@ -263,10 +263,10 @@ export class SchemaPreprocessor {
 
   private processDiscriminator(parent: Schema, schema: Schema, opts: any = {}) {
     const o = opts.discriminator;
-    const schemaObj = <SchemaObject>schema;
+    const schemaObj = <OpenAPIV3.CompositionSchemaObject>schema;
     const xOf = schemaObj.oneOf ? 'oneOf' : schemaObj.anyOf ? 'anyOf' : null;
 
-    if (xOf && schemaObj?.discriminator?.propertyName && !o.discriminator) {
+    if (xOf && schemaObj.discriminator?.propertyName && !o.discriminator) {
       const options = schemaObj[xOf].flatMap((refObject) => {
         if (refObject['$ref'] === undefined) {
           return [];