diff --git a/.changeset/beige-waves-wave.md b/.changeset/beige-waves-wave.md
new file mode 100644
index 000000000..690c37160
--- /dev/null
+++ b/.changeset/beige-waves-wave.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/partytown': patch
+---
+
+fix trailing slash with base path
diff --git a/packages/integrations/partytown/src/index.ts b/packages/integrations/partytown/src/index.ts
index eed0ab7c5..adeab75dd 100644
--- a/packages/integrations/partytown/src/index.ts
+++ b/packages/integrations/partytown/src/index.ts
@@ -17,6 +17,10 @@ type PartytownOptions =
 	  }
 	| undefined;
 
+function appendForwardSlash(str: string) {
+	return str.endsWith('/') ? str : str + '/';
+}
+
 export default function createPlugin(options: PartytownOptions): AstroIntegration {
 	let config: AstroConfig;
 	let partytownSnippetHtml: string;
@@ -26,7 +30,7 @@ export default function createPlugin(options: PartytownOptions): AstroIntegratio
 		name: '@astrojs/partytown',
 		hooks: {
 			'astro:config:setup': ({ config: _config, command, injectScript }) => {
-				const lib = `${_config.base}~partytown/`;
+				const lib = `${appendForwardSlash(_config.base)}~partytown/`;
 				const forward = options?.config?.forward || [];
 				const debug = options?.config?.debug || command === 'dev';
 				partytownSnippetHtml = partytownSnippet({ lib, debug, forward });