diff --git a/scripts/build.mjs b/scripts/build.mjs
index fef0f0a1..b8467760 100644
--- a/scripts/build.mjs
+++ b/scripts/build.mjs
@@ -213,7 +213,7 @@ async function buildJsLegacy(mainFile, extraFiles, importOverrides) {
                 "@babel/preset-env",
                 {
                     useBuiltIns: "entry",
-                    corejs: "3",
+                    corejs: "3.4",
                     targets: "IE 11",
                     // we provide our own promise polyfill (es6-promise)
                     // with support for synchronous flushing of