diff --git a/dev/integration_tests/flutter_gallery/web/index.html b/dev/integration_tests/flutter_gallery/web/index.html
index 328096a..23bcf28 100644
--- a/dev/integration_tests/flutter_gallery/web/index.html
+++ b/dev/integration_tests/flutter_gallery/web/index.html
@@ -12,11 +12,11 @@
   <meta name="apple-mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black">
   <meta name="apple-mobile-web-app-title" content="Flutter Gallery">
-  <link rel="apple-touch-icon" href="/icons/Icon-192.png">
-  <link rel="shortcut icon" type="image/png" href="/favicon.png"/>
+  <link rel="apple-touch-icon" href="icons/Icon-192.png">
+  <link rel="shortcut icon" type="image/png" href="favicon.png"/>
 
   <title>Flutter Gallery</title>
-  <link rel="manifest" href="/manifest.json">
+  <link rel="manifest" href="manifest.json">
 </head>
 <body>
   <!-- This script installs service_worker.js to provide PWA functionality to
@@ -25,7 +25,7 @@
   <script>
     if ('serviceWorker' in navigator) {
       window.addEventListener('load', function () {
-        navigator.serviceWorker.register('/flutter_service_worker.js');
+        navigator.serviceWorker.register('flutter_service_worker.js');
       });
     }
   </script>
diff --git a/packages/flutter_tools/lib/src/build_system/targets/web.dart b/packages/flutter_tools/lib/src/build_system/targets/web.dart
index 01c1c31..1efed88 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/web.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/web.dart
@@ -340,18 +340,26 @@
       .where((File file) => !file.path.endsWith('flutter_service_worker.js')
         && !globals.fs.path.basename(file.path).startsWith('.'))
       .toList();
-    // TODO(jonahwilliams): determine whether this needs to be made more efficient.
-    final Map<String, String> uriToHash = <String, String>{
-      for (File file in contents)
-        // Do not force caching of source maps.
-        if (!file.path.endsWith('main.dart.js.map'))
-        '/${globals.fs.path.toUri(globals.fs.path.relative(file.path, from: environment.outputDir.path)).toString()}':
-          md5.convert(await file.readAsBytes()).toString(),
-    };
+
+    final Map<String, String> urlToHash = <String, String>{};
+    for (final File file in contents) {
+      // Do not force caching of source maps.
+      if (file.path.endsWith('main.dart.js.map')) {
+        continue;
+      }
+      final String url = globals.fs.path.toUri(
+        globals.fs.path.relative(
+          file.path,
+          from: environment.outputDir.path),
+        ).toString();
+      final String hash = md5.convert(await file.readAsBytes()).toString();
+      urlToHash[url] = hash;
+    }
+
     final File serviceWorkerFile = environment.outputDir
       .childFile('flutter_service_worker.js');
     final Depfile depfile = Depfile(contents, <File>[serviceWorkerFile]);
-    final String serviceWorker = generateServiceWorker(uriToHash);
+    final String serviceWorker = generateServiceWorker(urlToHash);
     serviceWorkerFile
       .writeAsStringSync(serviceWorker);
     final DepfileService depfileService = DepfileService(
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
index f20b296..c56c39e 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
@@ -452,7 +452,7 @@
     expect(environment.outputDir.childFile('flutter_service_worker.js'), exists);
     // Contains file hash.
     expect(environment.outputDir.childFile('flutter_service_worker.js').readAsStringSync(),
-      contains('"/a/a.txt": "7fc56270e7a70fa81a5935b72eacbe29"'));
+      contains('"a/a.txt": "7fc56270e7a70fa81a5935b72eacbe29"'));
     expect(environment.buildDir.childFile('service_worker.d'), exists);
     // Depends on resource file.
     expect(environment.buildDir.childFile('service_worker.d').readAsStringSync(), contains('a/a.txt'));