diff --git a/packages/babel-preset-env/data/shipped-proposals.js b/packages/babel-preset-env/data/shipped-proposals.js
index 2376b388482a..e7fd15c3b1a3 100644
--- a/packages/babel-preset-env/data/shipped-proposals.js
+++ b/packages/babel-preset-env/data/shipped-proposals.js
@@ -2,9 +2,9 @@
 // These mappings represent the syntax proposals that have been
 // shipped by browsers, and are enabled by the `shippedProposals` option.
 
-const proposalPlugins = {
-  "proposal-numeric-separator": true
-};
+const proposalPlugins = new Set([
+  "proposal-numeric-separator",
+]);
 
 // use intermediary object to enforce alphabetical key order
 const pluginSyntaxObject = {
diff --git a/packages/babel-preset-env/src/utils.js b/packages/babel-preset-env/src/utils.js
index c7a330fe9f51..2630f5a1c428 100644
--- a/packages/babel-preset-env/src/utils.js
+++ b/packages/babel-preset-env/src/utils.js
@@ -28,10 +28,10 @@ export function intersection<T>(
 
 export function filterStageFromList(
   list: { [feature: string]: Targets },
-  stageList: { [feature: string]: boolean },
+  stageList: Set<string>,
 ) {
   return Object.keys(list).reduce((result, item) => {
-    if (!stageList[item]) {
+    if (!stageList.has(item)) {
       result[item] = list[item];
     }