diff --git a/package.json b/package.json
index bd0b5ce0932..3dc91e972e1 100644
--- a/package.json
+++ b/package.json
@@ -16,6 +16,7 @@
     },
     "./package.json": "./package.json"
   },
+  "sideEffects": false,
   "homepage": "https://emberjs.com/",
   "bugs": {
     "url": "https://github.com/emberjs/ember.js/issues"
diff --git a/rollup.config.mjs b/rollup.config.mjs
index ceee7e37ab1..6adf95e4b15 100644
--- a/rollup.config.mjs
+++ b/rollup.config.mjs
@@ -100,6 +100,9 @@ function sharedESMConfig({ input, debugMacrosMode, includePackageMeta = false })
   return {
     onLog: handleRollupWarnings,
     input,
+    treeshake: {
+      moduleSideEffects: moduleHasSideEffects,
+    },
     output: {
       format: 'es',
       dir: outputDir,
@@ -111,6 +114,18 @@ function sharedESMConfig({ input, debugMacrosMode, includePackageMeta = false })
   };
 }
 
+// `@glimmer/debug` declares `sideEffects: false` in its own package.json,
+// but rolldown loses that signal when files from it get co-bundled into
+// shared chunks alongside non-pure code. Re-asserting purity at the
+// chunk-level callback recovers ~8 KB raw on the hello-world bundle by
+// letting unused imports of `@glimmer/debug` content drop out of those
+// chunks. Add other packages here only after measuring an actual
+// reduction.
+function moduleHasSideEffects(id) {
+  if (id.includes('/packages/@glimmer/debug/')) return false;
+  return true;
+}
+
 function glimmerSyntaxESM() {
   return {
     onLog: handleRollupWarnings,