diff --git a/package-lock.json b/package-lock.json
index 477153a..ad16f30 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -12,7 +12,8 @@
         "@babel/generator": "^7.22.9",
         "@babel/parser": "^7.22.7",
         "@babel/traverse": "^7.22.8",
-        "@rollup/pluginutils": "^5.0.2"
+        "@rollup/pluginutils": "^5.0.2",
+        "joi": "^17.9.2"
       },
       "devDependencies": {
         "@commitlint/cli": "^17.6.7",
@@ -885,6 +886,19 @@
         "@jridgewell/sourcemap-codec": "^1.4.10"
       }
     },
+    "node_modules/@hapi/hoek": {
+      "version": "9.3.0",
+      "resolved": "https://registry.npmjs.org/@hapi/hoek/-/hoek-9.3.0.tgz",
+      "integrity": "sha512-/c6rf4UJlmHlC9b5BaNvzAcFv7HZ2QHaV0D4/HNlBdvFnvQq8RI4kYdhyPCl7Xj+oWvTWQ8ujhqS53LIgAe6KQ=="
+    },
+    "node_modules/@hapi/topo": {
+      "version": "5.1.0",
+      "resolved": "https://registry.npmjs.org/@hapi/topo/-/topo-5.1.0.tgz",
+      "integrity": "sha512-foQZKJig7Ob0BMAYBfcJk8d77QtOe7Wo4ox7ff1lQYoNNAb6jwcY1ncdoy2e9wQZzvNy7ODZCYJkK8kzmcAnAg==",
+      "dependencies": {
+        "@hapi/hoek": "^9.0.0"
+      }
+    },
     "node_modules/@isaacs/cliui": {
       "version": "8.0.2",
       "resolved": "https://registry.npmjs.org/@isaacs/cliui/-/cliui-8.0.2.tgz",
@@ -2477,6 +2491,24 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/@sideway/address": {
+      "version": "4.1.4",
+      "resolved": "https://registry.npmjs.org/@sideway/address/-/address-4.1.4.tgz",
+      "integrity": "sha512-7vwq+rOHVWjyXxVlR76Agnvhy8I9rpzjosTESvmhNeXOXdZZB15Fl+TI9x1SiHZH5Jv2wTGduSxFDIaq0m3DUw==",
+      "dependencies": {
+        "@hapi/hoek": "^9.0.0"
+      }
+    },
+    "node_modules/@sideway/formula": {
+      "version": "3.0.1",
+      "resolved": "https://registry.npmjs.org/@sideway/formula/-/formula-3.0.1.tgz",
+      "integrity": "sha512-/poHZJJVjx3L+zVD6g9KgHfYnb443oi7wLu/XKojDviHy6HOEOA6z1Trk5aR1dGcmPenJEgb2sK2I80LeS3MIg=="
+    },
+    "node_modules/@sideway/pinpoint": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/@sideway/pinpoint/-/pinpoint-2.0.0.tgz",
+      "integrity": "sha512-RNiOoTPkptFtSVzQevY/yWtZwf/RxyVnPy/OcA9HBM3MlGDnBEYL5B41H0MTn0Uec8Hi+2qUtTfG2WWZBmMejQ=="
+    },
     "node_modules/@sinclair/typebox": {
       "version": "0.27.8",
       "resolved": "https://registry.npmjs.org/@sinclair/typebox/-/typebox-0.27.8.tgz",
@@ -5626,6 +5658,18 @@
         "url": "https://github.com/chalk/supports-color?sponsor=1"
       }
     },
+    "node_modules/joi": {
+      "version": "17.9.2",
+      "resolved": "https://registry.npmjs.org/joi/-/joi-17.9.2.tgz",
+      "integrity": "sha512-Itk/r+V4Dx0V3c7RLFdRh12IOjySm2/WGPMubBT92cQvRfYZhPM2W0hZlctjj72iES8jsRCwp7S/cRmWBnJ4nw==",
+      "dependencies": {
+        "@hapi/hoek": "^9.0.0",
+        "@hapi/topo": "^5.0.0",
+        "@sideway/address": "^4.1.3",
+        "@sideway/formula": "^3.0.1",
+        "@sideway/pinpoint": "^2.0.0"
+      }
+    },
     "node_modules/js-tokens": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/js-tokens/-/js-tokens-4.0.0.tgz",
diff --git a/package.json b/package.json
index 3274b11..28b1a24 100644
--- a/package.json
+++ b/package.json
@@ -62,6 +62,7 @@
     "@babel/generator": "^7.22.9",
     "@babel/parser": "^7.22.7",
     "@babel/traverse": "^7.22.8",
-    "@rollup/pluginutils": "^5.0.2"
+    "@rollup/pluginutils": "^5.0.2",
+    "joi": "^17.9.2"
   }
 }
diff --git a/src/index.ts b/src/index.ts
index 5cc34fb..24569cd 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,6 +3,7 @@ import { parse } from "@babel/parser";
 import traverse from "@babel/traverse";
 import { createFilter } from "@rollup/pluginutils";
 import fs from "fs/promises";
+import Joi from "joi";
 import path from "path";
 import { Plugin } from "rollup";
 
@@ -11,15 +12,6 @@ const PREFIX = `\0${PLUGIN_NAME}:`;
 
 export type FilterPattern = string | RegExp | (string | RegExp)[];
 
-export function isFilterPattern(value: unknown): value is FilterPattern {
-	let tmp: unknown[];
-
-	if (Array.isArray(value)) tmp = value;
-	else tmp = [value];
-
-	return tmp.every((e) => typeof e === "string" || e instanceof RegExp);
-}
-
 export interface ExternalAssetsOptions {
 	/** A pattern, or array of patterns, to match files the plugin should ignore. */
 	include: FilterPattern;
@@ -29,6 +21,29 @@ export interface ExternalAssetsOptions {
 	resolve?: string;
 }
 
+const union = Joi.alternatives(Joi.string(), Joi.object().regex());
+const patternSchema = Joi.alternatives<FilterPattern>(
+	union,
+	Joi.array().items(union).min(1)
+);
+const optionsSchema = Joi.object<ExternalAssetsOptions>({
+	include: patternSchema.required(),
+	exclude: patternSchema,
+	resolve: Joi.string(),
+});
+
+function validate(arg: unknown): ExternalAssetsOptions {
+	const pattern = patternSchema.validate(arg);
+
+	if (!pattern.error) return { include: pattern.value };
+
+	const options = optionsSchema.validate(arg);
+
+	if (!options.error) return options.value;
+
+	throw new TypeError("Invalid argument");
+}
+
 /**
  * Make assets external but include them in the output.
  * @param options The options object.
@@ -41,15 +56,9 @@ function externalAssets(options: ExternalAssetsOptions): Plugin;
  */
 function externalAssets(pattern: FilterPattern): Plugin;
 
-function externalAssets(arg: FilterPattern | ExternalAssetsOptions): Plugin {
-	let idFilter: ReturnType<typeof createFilter>;
-
-	if (isFilterPattern(arg)) {
-		idFilter = createFilter(arg);
-	} else {
-		const { include, exclude, resolve } = arg;
-		idFilter = createFilter(include, exclude, { resolve });
-	}
+function externalAssets(arg: unknown): Plugin {
+	const { include, exclude, resolve } = validate(arg);
+	const idFilter = createFilter(include, exclude, { resolve });
 
 	return {
 		name: PLUGIN_NAME,