diff --git a/package.json b/package.json
index 221100d..5551310 100644
--- a/package.json
+++ b/package.json
@@ -16,7 +16,7 @@
     "test": "NODE_ENV=test mocha --exit"
   },
   "dependencies": {
-    "@asteasolutions/zod-to-openapi": "^4.8.0"
+    "@asteasolutions/zod-to-openapi": "^5.5.0"
   },
   "peerDependencies": {
     "express": "^5.0.0-beta.1",
diff --git a/src/openAPI.test.ts b/src/openAPI.test.ts
index c0fdd04..094af6e 100644
--- a/src/openAPI.test.ts
+++ b/src/openAPI.test.ts
@@ -92,7 +92,7 @@ describe("buildOpenAPIDocument", () => {
     const document = buildOpenAPIDocument({ config, routers, schemaPaths, errors, openApiVersion });
 
     expect(document.paths).to.have.property("/test");
-    expect(document.paths["/test"]).to.have.property("get");
+    expect(document.paths!["/test"]).to.have.property("get");
   });
 
   it("should include error responses if defined", () => {
@@ -160,8 +160,8 @@ describe("buildOpenAPIDocument", () => {
     const errors = { 401: "Unauthorized", 403: "Forbidden" };
 
     const document = buildOpenAPIDocument({ config, routers, schemaPaths, errors, openApiVersion });
-    const method = document.paths["/test"].get;
-    const responseSchema = method!.responses["200"].content["application/json"].schema;
+    const method = document.paths!["/test"].get;
+    const responseSchema = method!.responses!["200"].content["application/json"].schema;
 
     expect(responseSchema.$ref.includes("ResponseSchema")).to.be.true;
   });
@@ -186,7 +186,7 @@ describe("buildOpenAPIDocument", () => {
     const errors = { 401: "Unauthorized", 403: "Forbidden" };
 
     const document = buildOpenAPIDocument({ config, routers, schemaPaths, errors, openApiVersion });
-    const method = document.paths["/test"].get;
+    const method = document.paths!["/test"].get;
     // @ts-ignore
     const requestBodySchema = method!.requestBody?.content["application/json"].schema;
 
diff --git a/src/openAPI.ts b/src/openAPI.ts
index 6481f02..bb42fa5 100644
--- a/src/openAPI.ts
+++ b/src/openAPI.ts
@@ -1,10 +1,12 @@
 import {
   extendZodWithOpenApi,
-  OpenAPIGenerator,
+  OpenApiGeneratorV3,
+  OpenApiGeneratorV31,
   OpenAPIRegistry,
   ResponseConfig,
   RouteConfig,
 } from "@asteasolutions/zod-to-openapi";
+import { OpenApiVersion } from "@asteasolutions/zod-to-openapi/dist/openapi-generator";
 import { RequestHandler, Router } from "express";
 import type { ComponentsObject } from "openapi3-ts/oas30";
 import { z, ZodArray, ZodEffects, ZodObject } from "zod";
@@ -13,19 +15,19 @@ import { ErrorResponse } from "./schemas";
 
 extendZodWithOpenApi(z);
 
-export type OpenAPIDocument = ReturnType<OpenAPIGenerator["generateDocument"]>;
-export type OpenAPIComponents = ReturnType<OpenAPIGenerator["generateComponents"]>;
-export type OpenAPIConfig = Parameters<OpenAPIGenerator["generateDocument"]>[0];
-export type OpenApiVersion = ConstructorParameters<typeof OpenAPIGenerator>[1];
+export type OpenAPIDocument = ReturnType<OpenApiGeneratorV3["generateDocument"]>;
+export type OpenAPIV31Document = ReturnType<OpenApiGeneratorV31["generateDocument"]>;
+export type OpenAPIComponents = ReturnType<OpenApiGeneratorV3["generateComponents"]>;
+export type OpenAPIConfig = Parameters<OpenApiGeneratorV3["generateDocument"]>[0];
 
 export function buildOpenAPIDocument(args: {
-  config: OpenAPIConfig;
+  config: Omit<OpenAPIConfig, "openapi">;
   routers: Router[];
   schemaPaths: string[];
   errors: { 401?: string; 403?: string };
   securitySchemes?: ComponentsObject["securitySchemes"];
   openApiVersion: OpenApiVersion;
-}): OpenAPIDocument {
+}): OpenAPIDocument | OpenAPIV31Document {
   const { config, routers, schemaPaths, securitySchemes, errors, openApiVersion } = args;
   const registry = new OpenAPIRegistry();
   // Attach all of the Zod schemas to the OpenAPI specification
@@ -189,8 +191,11 @@ export function buildOpenAPIDocument(args: {
     registry.registerPath(openapiRouteConfig);
   });
 
-  const generator = new OpenAPIGenerator(registry.definitions, openApiVersion);
-  const openapiJSON = generator.generateDocument(config);
+  const generator =
+    openApiVersion === "3.1.0"
+      ? new OpenApiGeneratorV31(registry.definitions)
+      : new OpenApiGeneratorV3(registry.definitions);
+  const openapiJSON = generator.generateDocument({ ...config, openapi: openApiVersion });
 
   // Attach the security schemes provided
   if (securitySchemes) {
@@ -200,17 +205,19 @@ export function buildOpenAPIDocument(args: {
 
   // Verify that none of the "parameters" are appearing as optional, which is invalid
   // in the official OpenAPI spec and unsupported by readme.io
-  for (const [route, impl] of Object.entries(openapiJSON.paths)) {
-    for (const key of Object.keys(impl)) {
-      const method = key as keyof typeof impl;
-      for (const param of impl[method].parameters || []) {
-        if (param.required === false && param.in === "path") {
-          param.required = true;
-          console.warn(
-            `OpenAPI Warning: The route ${route} has an optional parameter ${param.name} in the path. ` +
-              `Optional parameters in the route path are not supported by readme.io. Make the parameter required ` +
-              `or split the route definition into two separate ones, one with the param and one without.`,
-          );
+  if (openapiJSON.paths) {
+    for (const [route, impl] of Object.entries(openapiJSON.paths)) {
+      for (const key of Object.keys(impl)) {
+        const method = key as keyof typeof impl;
+        for (const param of impl[method].parameters || []) {
+          if (param.required === false && param.in === "path") {
+            param.required = true;
+            console.warn(
+              `OpenAPI Warning: The route ${route} has an optional parameter ${param.name} in the path. ` +
+                `Optional parameters in the route path are not supported by readme.io. Make the parameter required ` +
+                `or split the route definition into two separate ones, one with the param and one without.`,
+            );
+          }
         }
       }
     }
diff --git a/yarn.lock b/yarn.lock
index fa3c167..f71025e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2,10 +2,10 @@
 # yarn lockfile v1
 
 
-"@asteasolutions/zod-to-openapi@^4.8.0":
-  version "4.8.0"
-  resolved "https://registry.yarnpkg.com/@asteasolutions/zod-to-openapi/-/zod-to-openapi-4.8.0.tgz#34c29228c5cd0098a534b3536c9f486fafca2cc1"
-  integrity sha512-FQlBeHIhSoEhjddAWD1v2zbeBESfTdaAVQuUr0RY9t0rN8ogoEaGirv2Ne8kQQTAVGydJzUMAOIlPULEOQDoeA==
+"@asteasolutions/zod-to-openapi@^5.5.0":
+  version "5.5.0"
+  resolved "https://registry.yarnpkg.com/@asteasolutions/zod-to-openapi/-/zod-to-openapi-5.5.0.tgz#f3be8f1e97ece0fcef2e6ff5e9230da8138d20a6"
+  integrity sha512-d5HwrvM6dOKr3XdeF+DmashGvfEc+1oiEfbscugsiwSTrFtuMa7ETpW9sTNnVgn+hJaz+PRxPQUYD7q9/5dUig==
   dependencies:
     openapi3-ts "^4.1.2"