diff --git a/.changeset/mean-bags-shave.md b/.changeset/mean-bags-shave.md
new file mode 100644
index 000000000000..88263fa05ec8
--- /dev/null
+++ b/.changeset/mean-bags-shave.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a bug where `astro.config.mts` and `astro.config.cts` weren't reloading the dev server upon modifications.
diff --git a/packages/astro/src/core/dev/restart.ts b/packages/astro/src/core/dev/restart.ts
index 30821362c744..b7eab38af66b 100644
--- a/packages/astro/src/core/dev/restart.ts
+++ b/packages/astro/src/core/dev/restart.ts
@@ -30,7 +30,7 @@ async function createRestartedContainer(
 	return newContainer;
 }
 
-const configRE = /.*astro.config.(?:mjs|cjs|js|ts)$/;
+const configRE = /.*astro.config.(?:mjs|mts|cjs|cts|js|ts)$/;
 
 function shouldRestartContainer(
 	{ settings, inlineConfig, restartInFlight }: Container,