diff --git a/pkgs/test/CHANGELOG.md b/pkgs/test/CHANGELOG.md
index cb77b6a..b5cb03e 100644
--- a/pkgs/test/CHANGELOG.md
+++ b/pkgs/test/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.24.10-wip
+
+* Handle paths with leading `/` when spawning test isolates.
+
 ## 1.24.9
 
 * Update the vm_service constraint to allow version `13.x`.
diff --git a/pkgs/test/pubspec.yaml b/pkgs/test/pubspec.yaml
index 85c8ccc..12f2a63 100644
--- a/pkgs/test/pubspec.yaml
+++ b/pkgs/test/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 1.24.9
+version: 1.24.10-wip
 description: >-
   A full featured library for writing and running Dart tests across platforms.
 repository: https://github.com/dart-lang/test/tree/master/pkgs/test
@@ -35,7 +35,7 @@
 
   # Use an exact version until the test_api and test_core package are stable.
   test_api: 0.6.1
-  test_core: 0.5.9
+  test_core: 0.5.10
 
   typed_data: ^1.3.0
   web_socket_channel: ^2.0.0
diff --git a/pkgs/test_core/CHANGELOG.md b/pkgs/test_core/CHANGELOG.md
index e71cd13..808ff03 100644
--- a/pkgs/test_core/CHANGELOG.md
+++ b/pkgs/test_core/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.5.10-wip
+
+* Handle paths with leading `/` when spawning test isolates.
+
 ## 0.5.9
 
 * Update the vm_service constraint to allow version `13.x`.
diff --git a/pkgs/test_core/lib/src/runner/configuration/args.dart b/pkgs/test_core/lib/src/runner/configuration/args.dart
index fac1224..47209c8 100644
--- a/pkgs/test_core/lib/src/runner/configuration/args.dart
+++ b/pkgs/test_core/lib/src/runner/configuration/args.dart
@@ -199,18 +199,7 @@
     }
   }
   final uri = Uri.parse(option);
-  // Decode the path segment. Specifically, on github actions back slashes on
-  // windows end up being encoded into the URI instead of converted into forward
-  // slashes.
-  var path = Uri.decodeComponent(uri.path);
-  // Strip out the leading slash before the drive letter on windows.
-  if (Platform.isWindows &&
-      path.startsWith('/') &&
-      path.length >= 3 &&
-      path[2] == ':') {
-    path = path.substring(1);
-  }
-
+  final path = Uri.decodeComponent(uri.path).stripDriveLetterLeadingSlash;
   final names = uri.queryParametersAll['name'];
   final fullName = uri.queryParameters['full-name'];
   final line = uri.queryParameters['line'];
diff --git a/pkgs/test_core/lib/src/runner/vm/platform.dart b/pkgs/test_core/lib/src/runner/vm/platform.dart
index 9ab7892..6a57c31 100644
--- a/pkgs/test_core/lib/src/runner/vm/platform.dart
+++ b/pkgs/test_core/lib/src/runner/vm/platform.dart
@@ -263,8 +263,9 @@
 
   Future<Isolate> _spawnPrecompiledIsolate(String testPath, SendPort message,
       String precompiledPath, Compiler compiler) async {
-    testPath =
-        _absolute('${p.join(precompiledPath, testPath)}.vm_test.dart').path;
+    testPath = _absolute('${p.join(precompiledPath, testPath)}.vm_test.dart')
+        .path
+        .stripDriveLetterLeadingSlash;
     switch (compiler) {
       case Compiler.kernel:
         var dillTestpath =
diff --git a/pkgs/test_core/lib/src/util/io.dart b/pkgs/test_core/lib/src/util/io.dart
index 98bb23b..d6be843 100644
--- a/pkgs/test_core/lib/src/util/io.dart
+++ b/pkgs/test_core/lib/src/util/io.dart
@@ -247,3 +247,19 @@
     }
   }
 }
+
+extension WindowsFilePaths on String {
+  /// Strip out the leading slash before the drive letter on windows.
+  ///
+  /// In some windows environments full paths get passed with `/` before the
+  /// drive letter. Normalize paths to exclude this slash when it exists.
+  String get stripDriveLetterLeadingSlash {
+    if (Platform.isWindows &&
+        startsWith('/') &&
+        length >= 3 &&
+        this[2] == ':') {
+      return substring(1);
+    }
+    return this;
+  }
+}
diff --git a/pkgs/test_core/pubspec.yaml b/pkgs/test_core/pubspec.yaml
index a3e6fd1..cc36502 100644
--- a/pkgs/test_core/pubspec.yaml
+++ b/pkgs/test_core/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test_core
-version: 0.5.9
+version: 0.5.10-wip
 description: A basic library for writing tests and running them on the VM.
 repository: https://github.com/dart-lang/test/tree/master/pkgs/test_core