diff --git a/packages/vite/src/node/plugins/css.ts b/packages/vite/src/node/plugins/css.ts
index 0e97c247cf01f8..445c13fd91ae0b 100644
--- a/packages/vite/src/node/plugins/css.ts
+++ b/packages/vite/src/node/plugins/css.ts
@@ -912,7 +912,9 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           css += chunkCSSMap.get(chunk.preliminaryFileName) ?? ''
         }
 
-        for (const chunkName of chunkCSSMap.keys())
+        // sorted chunk names to guarantee output order (deterministic output)
+        const chunkNames = [...chunkCSSMap.keys()].sort()
+        for (const chunkName of chunkNames)
           collect(prelimaryNameToChunkMap.get(chunkName)?.fileName ?? '')
 
         return css