diff --git a/src/author.ts b/src/author.ts
index f6d640f..adda90c 100644
--- a/src/author.ts
+++ b/src/author.ts
@@ -42,7 +42,7 @@ export class Author {
 		this.ipAddress = options.ipAddress ?? "";
 		this.name = options.name ?? "";
 		this.role = options.role ?? "";
-		this.url = options.url ? new URL(options.url) : null;
+		this.url = options.url && URL.canParse(options.url) ? new URL(options.url) : null;
 		this.userAgent = options.userAgent ?? "";
 	}
 
diff --git a/src/blog.ts b/src/blog.ts
index fa8b4e5..728a1f8 100644
--- a/src/blog.ts
+++ b/src/blog.ts
@@ -25,7 +25,7 @@ export class Blog {
 	constructor(options: Partial<BlogOptions> = {}) {
 		this.charset = options.charset ?? "";
 		this.languages = options.languages ?? [];
-		this.url = options.url ? new URL(options.url) : null;
+		this.url = options.url && URL.canParse(options.url) ? new URL(options.url) : null;
 	}
 
 	/**
diff --git a/src/client.ts b/src/client.ts
index f89234b..cbe1341 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -49,11 +49,11 @@ export class Client {
 	 * @param options An object providing values to initialize this instance.
 	 */
 	constructor(apiKey: string, blog: Blog, options: Partial<ClientOptions> = {}) {
-		const {baseUrl = "https://rest.akismet.com"} = options;
+		const {baseUrl = ""} = options;
 		const url = baseUrl instanceof URL ? baseUrl.href : baseUrl;
 
 		this.apiKey = apiKey;
-		this.baseUrl = new URL(url.endsWith("/") ? url : `${url}/`);
+		this.baseUrl = new URL(URL.canParse(url) ? (url.endsWith("/") ? url : `${url}/`) : "https://rest.akismet.com/");
 		this.blog = blog;
 		this.isTest = options.isTest ?? false;
 		this.userAgent = options.userAgent ?? `${navigator.userAgent} | Akismet/${Client.#version}`;
diff --git a/src/comment.ts b/src/comment.ts
index 7f66fd0..c944c11 100644
--- a/src/comment.ts
+++ b/src/comment.ts
@@ -59,10 +59,10 @@ export class Comment {
 		this.content = options.content ?? "";
 		this.context = options.context ?? [];
 		this.date = options.date ?? null;
-		this.permalink = options.permalink ? new URL(options.permalink) : null;
+		this.permalink = options.permalink && URL.canParse(options.permalink) ? new URL(options.permalink) : null;
 		this.postModified = options.postModified ?? null;
 		this.recheckReason = options.recheckReason ?? "";
-		this.referrer = options.referrer ? new URL(options.referrer) : null;
+		this.referrer = options.referrer && URL.canParse(options.referrer) ? new URL(options.referrer) : null;
 		this.type = options.type ?? "";
 	}