diff --git a/.changeset/tidy-peas-accept.md b/.changeset/tidy-peas-accept.md
new file mode 100644
index 0000000000..fa580f0734
--- /dev/null
+++ b/.changeset/tidy-peas-accept.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes preview server `trailingSlash` handling for request URLs with query strings
diff --git a/packages/astro/src/core/preview/vite-plugin-astro-preview.ts b/packages/astro/src/core/preview/vite-plugin-astro-preview.ts
index 9faabe29b2..b07b88b7ad 100644
--- a/packages/astro/src/core/preview/vite-plugin-astro-preview.ts
+++ b/packages/astro/src/core/preview/vite-plugin-astro-preview.ts
@@ -24,7 +24,8 @@ export function vitePluginAstroPreview(settings: AstroSettings): Plugin {
 					return;
 				}
 
-				const pathname = stripBase(req.url!, base);
+				const strippedPathname = stripBase(req.url!, base);
+        const pathname = new URL(strippedPathname, 'https://a.b').pathname
 				const isRoot = pathname === '/';
 
 				// Validate trailingSlash