diff --git a/packages/angular/build/src/builders/karma/application_builder.ts b/packages/angular/build/src/builders/karma/application_builder.ts
index bfe7af7711..7651ecaaff 100644
--- a/packages/angular/build/src/builders/karma/application_builder.ts
+++ b/packages/angular/build/src/builders/karma/application_builder.ts
@@ -438,7 +438,8 @@ async function initializeApplication(
   await writeTestFiles(buildOutput.files, buildOptions.outputPath);
 
   // We need to add this to the beginning *after* the testing framework has
-  // prepended its files.
+  // prepended its files. The output path is required for each since they are
+  // added later in the test process via a plugin.
   const polyfillsFile: FilePattern = {
     pattern: `${outputPath}/polyfills.js`,
     included: true,
@@ -454,12 +455,14 @@ async function initializeApplication(
     watched: false,
   };
 
+  karmaOptions.basePath = outputPath;
+
   karmaOptions.files ??= [];
   if (options.scripts?.length) {
     // This should be more granular to support named bundles.
     // However, it replicates the behavior of the Karma Webpack-based builder.
     karmaOptions.files.push({
-      pattern: `${outputPath}/scripts.js`,
+      pattern: `scripts.js`,
       watched: false,
       type: 'js',
     });
@@ -467,18 +470,18 @@ async function initializeApplication(
 
   karmaOptions.files.push(
     // Serve global setup script.
-    { pattern: `${outputPath}/${mainName}.js`, type: 'module', watched: false },
+    { pattern: `${mainName}.js`, type: 'module', watched: false },
     // Serve all source maps.
-    { pattern: `${outputPath}/*.map`, included: false, watched: false },
+    { pattern: `*.map`, included: false, watched: false },
     // These are the test entrypoints.
-    { pattern: `${outputPath}/spec-*.js`, type: 'module', watched: false },
+    { pattern: `spec-*.js`, type: 'module', watched: false },
   );
 
   if (hasChunkOrWorkerFiles(buildOutput.files)) {
     karmaOptions.files.push(
       // Allow loading of chunk-* files but don't include them all on load.
       {
-        pattern: `${outputPath}/{chunk,worker}-*.js`,
+        pattern: `{chunk,worker}-*.js`,
         type: 'module',
         included: false,
         watched: false,
@@ -488,7 +491,7 @@ async function initializeApplication(
 
   if (options.styles?.length) {
     // Serve CSS outputs on page load, these are the global styles.
-    karmaOptions.files.push({ pattern: `${outputPath}/*.css`, type: 'css', watched: false });
+    karmaOptions.files.push({ pattern: `*.css`, type: 'css', watched: false });
   }
 
   const parsedKarmaConfig: Config & ConfigOptions = await karma.config.parseConfig(
diff --git a/tests/legacy-cli/e2e/tests/test/test-sourcemap.ts b/tests/legacy-cli/e2e/tests/test/test-sourcemap.ts
index 797aba88e1..e75e214a24 100644
--- a/tests/legacy-cli/e2e/tests/test/test-sourcemap.ts
+++ b/tests/legacy-cli/e2e/tests/test/test-sourcemap.ts
@@ -20,7 +20,7 @@ export default async function () {
     throw new Error('ng test should have failed.');
   } catch (error) {
     assertIsError(error);
-    assert.match(error.message, /src\/app\/app\.component\.spec\.ts/);
+    assert.match(error.message, /\(src\/app\/app\.component\.spec\.ts:3:27/);
     assert.doesNotMatch(error.message, /_karma_webpack_/);
   }