diff --git a/packages/flutter_tools/lib/src/html_utils.dart b/packages/flutter_tools/lib/src/html_utils.dart
index 259f038739..ad394aaa90 100644
--- a/packages/flutter_tools/lib/src/html_utils.dart
+++ b/packages/flutter_tools/lib/src/html_utils.dart
@@ -70,8 +70,9 @@ class IndexHtml {
     if (serviceWorkerVersion != null) {
       _content = _content
           .replaceFirst(
-            'var serviceWorkerVersion = null',
-            'var serviceWorkerVersion = "$serviceWorkerVersion"',
+            // Support older `var` syntax as well as new `const` syntax
+            RegExp('(const|var) serviceWorkerVersion = null'),
+            'const serviceWorkerVersion = "$serviceWorkerVersion"',
           )
           // This is for legacy index.html that still uses the old service
           // worker loading mechanism.
diff --git a/packages/flutter_tools/templates/app_shared/web/index.html.tmpl b/packages/flutter_tools/templates/app_shared/web/index.html.tmpl
index 6d9aa4d08c..2e1847c4a7 100644
--- a/packages/flutter_tools/templates/app_shared/web/index.html.tmpl
+++ b/packages/flutter_tools/templates/app_shared/web/index.html.tmpl
@@ -34,7 +34,7 @@
 
   <script>
     // The value below is injected by flutter build, do not touch.
-    var serviceWorkerVersion = null;
+    const serviceWorkerVersion = null;
   </script>
   <!-- This script adds the flutter initialization JS code -->
   <script src="flutter.js" defer></script>
diff --git a/packages/flutter_tools/test/general.shard/html_utils_test.dart b/packages/flutter_tools/test/general.shard/html_utils_test.dart
index b8c10525ca..83a5f0c1a6 100644
--- a/packages/flutter_tools/test/general.shard/html_utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/html_utils_test.dart
@@ -31,6 +31,28 @@ const String htmlSample2 = '''
   <meta charset="utf-8">
   <link rel="icon" type="image/png" href="favicon.png"/>
 </head>
+<body>
+  <div></div>
+  <script src="main.dart.js"></script>
+  <script>
+    const serviceWorkerVersion = null;
+  </script>
+  <script>
+    navigator.serviceWorker.register('flutter_service_worker.js');
+  </script>
+</body>
+</html>
+''';
+
+const String htmlSampleLegacyVar = '''
+<!DOCTYPE html>
+<html>
+<head>
+  <title></title>
+  <base href="$kBaseHrefPlaceholder">
+  <meta charset="utf-8">
+  <link rel="icon" type="image/png" href="favicon.png"/>
+</head>
 <body>
   <div></div>
   <script src="main.dart.js"></script>
@@ -61,7 +83,7 @@ String htmlSample2Replaced({
   <div></div>
   <script src="main.dart.js"></script>
   <script>
-    var serviceWorkerVersion = "$serviceWorkerVersion";
+    const serviceWorkerVersion = "$serviceWorkerVersion";
   </script>
   <script>
     navigator.serviceWorker.register('flutter_service_worker.js?v=$serviceWorkerVersion');
@@ -127,6 +149,21 @@ void main() {
     );
   });
 
+  test('applies substitutions with legacy var version syntax', () {
+    final IndexHtml indexHtml = IndexHtml(htmlSampleLegacyVar);
+    indexHtml.applySubstitutions(
+      baseHref: '/foo/333/',
+      serviceWorkerVersion: 'v123xyz',
+    );
+    expect(
+      indexHtml.content,
+      htmlSample2Replaced(
+        baseHref: '/foo/333/',
+        serviceWorkerVersion: 'v123xyz',
+      ),
+    );
+  });
+
   test('re-parses after substitutions', () {
     final IndexHtml indexHtml = IndexHtml(htmlSample2);
     expect(indexHtml.getBaseHref(), ''); // Placeholder base href.
diff --git a/packages/flutter_tools/test/web.shard/test_data/hot_reload_index_html_samples.dart b/packages/flutter_tools/test/web.shard/test_data/hot_reload_index_html_samples.dart
index 9812b34a9c..b1d5d2a18d 100644
--- a/packages/flutter_tools/test/web.shard/test_data/hot_reload_index_html_samples.dart
+++ b/packages/flutter_tools/test/web.shard/test_data/hot_reload_index_html_samples.dart
@@ -79,7 +79,7 @@ found in the LICENSE file. -->
   application. For more information, see:
   https://developers.google.com/web/fundamentals/primers/service-workers -->
   <script>
-    var serviceWorkerVersion = null;
+    const serviceWorkerVersion = null;
     var scriptLoaded = false;
     function loadMainDartJs() {
       if (scriptLoaded) {
@@ -165,7 +165,7 @@ found in the LICENSE file. -->
   <link rel="manifest" href="manifest.json">
   <script>
     // The value below is injected by flutter build, do not touch.
-    var serviceWorkerVersion = null;
+    const serviceWorkerVersion = null;
   </script>
   <!-- This script adds the flutter initialization JS code -->
   <script src="flutter.js" defer></script>
