diff --git a/.changeset/metal-lions-try.md b/.changeset/metal-lions-try.md
new file mode 100644
index 000000000..c70a2f872
--- /dev/null
+++ b/.changeset/metal-lions-try.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Bugfix: do not override user `alias` passed into snowpack config
diff --git a/packages/astro/src/runtime.ts b/packages/astro/src/runtime.ts
index a12f5d4fe..a8a322f84 100644
--- a/packages/astro/src/runtime.ts
+++ b/packages/astro/src/runtime.ts
@@ -422,8 +422,8 @@ async function createSnowpack(astroConfig: AstroConfig, options: CreateSnowpackO
   });
 
   const polyfillNode = (snowpackConfig.packageOptions as any).polyfillNode as boolean;
-  if(!polyfillNode) {
-    snowpackConfig.alias = Object.fromEntries(nodeBuiltinsMap);
+  if (!polyfillNode) {
+    snowpackConfig.alias = Object.assign({}, Object.fromEntries(nodeBuiltinsMap), snowpackConfig.alias ?? {});
   }
 
   snowpack = await startSnowpackServer(