diff --git a/.changeset/dev-server-node18-close.md b/.changeset/dev-server-node18-close.md
new file mode 100644
index 000000000..1b5b4f2f0
--- /dev/null
+++ b/.changeset/dev-server-node18-close.md
@@ -0,0 +1,5 @@
+---
+"@callstack/repack-dev-server": patch
+---
+
+Fix dev server shutdown hanging on Node 18 with fastify 5.12+ by force-closing open connections on stop
diff --git a/apps/tester-app/rspack.config.mjs b/apps/tester-app/rspack.config.mjs
index 80bd93db2..641ffbb37 100644
--- a/apps/tester-app/rspack.config.mjs
+++ b/apps/tester-app/rspack.config.mjs
@@ -2,7 +2,12 @@ import path from 'node:path';
 import * as Repack from '@callstack/repack';
 import { NativeWindPlugin } from '@callstack/repack-plugin-nativewind';
 import { ReanimatedPlugin } from '@callstack/repack-plugin-reanimated';
-import { RsdoctorRspackPlugin } from '@rsdoctor/rspack-plugin';
+
+// Rsdoctor (through rslog) throws on import under Node < 20, so only load it
+// when it's actually enabled to keep the Node 18 test matrix working.
+const { RsdoctorRspackPlugin } = process.env.RSDOCTOR
+  ? await import('@rsdoctor/rspack-plugin')
+  : {};
 
 const dirname = Repack.getDirname(import.meta.url);
 
diff --git a/packages/dev-server/src/createServer.ts b/packages/dev-server/src/createServer.ts
index 404d956d3..5c1805c91 100644
--- a/packages/dev-server/src/createServer.ts
+++ b/packages/dev-server/src/createServer.ts
@@ -28,6 +28,10 @@ export async function createServer(config: Server.Config) {
 
   /** Fastify instance powering the development server. */
   const instance = Fastify({
+    // Since fastify 5.12 the default ('idle') leaves idle keep-alive sockets
+    // to `server.close()`, which only closes them on Node 19+. Force-closing
+    // keeps `stop()` from hanging on Node 18.
+    forceCloseConnections: true,
     disableRequestLogging: options.disableRequestLogging,
     logger: {
       level: 'trace',