diff --git a/.changeset/early-kangaroos-invent.md b/.changeset/early-kangaroos-invent.md
new file mode 100644
index 000000000000..e2de069196aa
--- /dev/null
+++ b/.changeset/early-kangaroos-invent.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/cloudflare': patch
+---
+
+fix `config.base` trimming logic for cloudflare integration `_routes.json` generation
diff --git a/packages/integrations/cloudflare/src/index.ts b/packages/integrations/cloudflare/src/index.ts
index 2f182d6043a0..6cdfdd96cbbd 100644
--- a/packages/integrations/cloudflare/src/index.ts
+++ b/packages/integrations/cloudflare/src/index.ts
@@ -156,7 +156,7 @@ export default function createIntegration(args?: Options): AstroIntegration {
 						let pagePath = prependForwardSlash(page.pathname);
 						if (_config.base !== '/') {
 							const base = _config.base.endsWith('/')
-								? _config.base.substring(0, -1)
+								? _config.base.slice(0, -1)
 								: _config.base;
 							pagePath = `${base}${pagePath}`;
 						}