diff --git a/testing/runner.ts b/testing/runner.ts
index 85d0c70ab94c..0839f7bd6414 100755
--- a/testing/runner.ts
+++ b/testing/runner.ts
@@ -7,6 +7,7 @@ import {
   glob,
   ExpandGlobOptions
 } from "../fs/mod.ts";
+import { isWindows } from "../fs/path/constants.ts";
 import { isAbsolute, join } from "../fs/path/mod.ts";
 import { RunTestsOptions, runTests } from "./mod.ts";
 const { DenoError, ErrorKind, args, cwd, exit } = Deno;
@@ -55,6 +56,10 @@ function partition(
   );
 }
 
+function filePathToUrl(path: string): string {
+  return `file://${isWindows ? "/" : ""}${path.replace(/\\/g, "/")}`;
+}
+
 function expandDirectory(dir: string, options: ExpandGlobOptions): WalkInfo[] {
   return DIR_GLOBS.flatMap((s: string): WalkInfo[] => [
     ...expandGlobSync(s, { ...options, root: dir })
@@ -108,10 +113,7 @@ export async function findTestModules(
 
   const matchedUrls = includeUrls.filter(notExcludedUrl);
 
-  return [
-    ...matchedPaths.map((path: string): string => `file://${path}`),
-    ...matchedUrls
-  ];
+  return [...matchedPaths.map(filePathToUrl), ...matchedUrls];
 }
 
 export interface RunTestModulesOptions extends RunTestsOptions {