diff --git a/src/utils/__tests__/test-common.test.ts b/src/utils/__tests__/test-common.test.ts
index 991cb85a..a95a552d 100644
--- a/src/utils/__tests__/test-common.test.ts
+++ b/src/utils/__tests__/test-common.test.ts
@@ -197,6 +197,51 @@ describe('createTestExecutor', () => {
     expect(runTestsIndex).toBeGreaterThan(-1);
     expect(finalSummaryIndex).toBeGreaterThan(runTestsIndex);
   });
+  it('uses the source test phase for prepared products containing multiple simulator platforms', async () => {
+    const commands: string[][] = [];
+    const executor: CommandExecutor = async (command) => {
+      commands.push(command);
+      if (command.at(-1) === 'build-for-testing') {
+        const testProductsIndex = command.indexOf('-testProductsPath');
+        const testProductsPath = command[testProductsIndex + 1]!;
+        mkdirSync(join(testProductsPath, 'Tests', '0'), { recursive: true });
+        writeFileSync(
+          join(testProductsPath, 'Tests', '0', 'Weather.xctestrun'),
+          `<?xml version="1.0"?><plist><dict><key>TestConfigurations</key><array><dict><key>TestTargets</key><array><dict><key>DependentProductPaths</key><array><string>__TESTROOT__/Debug-iphonesimulator/Weather.app</string><string>__TESTROOT__/Debug-watchsimulator/WatchTests.xctest</string></array></dict></array></dict></array></dict></plist>`,
+        );
+      }
+      return createSuccessfulCommandResponse();
+    };
+
+    const executeTest = createTestExecutor(executor, {
+      preflight: createPreflight(),
+      toolName: 'test_sim',
+      target: 'simulator',
+      request: {
+        scheme: 'Weather',
+        projectPath: 'Weather.xcodeproj',
+        configuration: 'Debug',
+        platform: XcodePlatform.iOSSimulator,
+      },
+    });
+
+    await executeTest(
+      {
+        projectPath: 'Weather.xcodeproj',
+        scheme: 'Weather',
+        configuration: 'Debug',
+        simulatorId: 'A2C64636-37E9-4B68-B872-E7F0A82A5670',
+        platform: XcodePlatform.iOSSimulator,
+      },
+      new DefaultStreamingExecutionContext(),
+    );
+
+    expect(commands).toHaveLength(2);
+    expect(commands[1]).toContain('-project');
+    expect(commands[1]).toContain('-scheme');
+    expect(commands[1]).toContain('-derivedDataPath');
+    expect(commands[1]).not.toContain('-testProductsPath');
+  });
 
   it('injects a workspace-scoped default result bundle path for macOS test commands', async () => {
     const commands: string[][] = [];
diff --git a/src/utils/test-common.ts b/src/utils/test-common.ts
index 8dab5285..123c9169 100644
--- a/src/utils/test-common.ts
+++ b/src/utils/test-common.ts
@@ -8,6 +8,7 @@ import * as path from 'node:path';
 import { log } from './logger.ts';
 import { constructDestinationString, XcodePlatform } from './xcode.ts';
 import { executeXcodeBuildCommand } from './build/index.ts';
+import type { BuildCommandResult } from './build/index.ts';
 import { extractTestFailuresFromXcresult } from './xcresult-test-failures.ts';
 
 import { normalizeTestRunnerEnv } from './environment.ts';
@@ -23,6 +24,7 @@ import {
 } from './result-bundle-path.ts';
 import {
   createDefaultTestProductsPath,
+  hasMultipleSimulatorPlatforms,
   markTestProductsPathCompleted,
 } from './test-products-path.ts';
 import { resolvePathFromCwd } from './path.ts';
@@ -317,17 +319,36 @@ export function createTestExecutor(
         message: 'Running tests',
       });
 
-      let testWithoutBuildingResult: PreparedTestCommandResult;
+      let testWithoutBuildingResult: PreparedTestCommandResult | BuildCommandResult;
       try {
-        testWithoutBuildingResult = await executePreparedTestCommand(
-          { ...params, testProductsPath },
-          filterPreparedTestExtraArgs(executionPlan.testArgs),
-          resultBundlePath,
-          executor,
-          execOpts,
-          started.pipeline,
-          getPreparedTestDestinationArgs(executionPlan.testArgs),
-        );
+        const usesMultipleSimulatorPlatforms =
+          await hasMultipleSimulatorPlatforms(testProductsPath);
+        testWithoutBuildingResult = usesMultipleSimulatorPlatforms
+          ? await executeXcodeBuildCommand(
+              {
+                ...params,
+                extraArgs: [
+                  ...filterPreparedTestExtraArgs(executionPlan.testArgs),
+                  '-resultBundlePath',
+                  resultBundlePath,
+                ],
+              },
+              platformOptions,
+              params.preferXcodebuild,
+              'test-without-building',
+              executor,
+              execOpts,
+              started.pipeline,
+            )
+          : await executePreparedTestCommand(
+              { ...params, testProductsPath },
+              filterPreparedTestExtraArgs(executionPlan.testArgs),
+              resultBundlePath,
+              executor,
+              execOpts,
+              started.pipeline,
+              getPreparedTestDestinationArgs(executionPlan.testArgs),
+            );
       } finally {
         markTestProductsPathCompleted(testProductsPath);
         if (shouldUseDefaultResultBundlePath) {
diff --git a/src/utils/test-products-path.ts b/src/utils/test-products-path.ts
index 2287cf1c..c061fd45 100644
--- a/src/utils/test-products-path.ts
+++ b/src/utils/test-products-path.ts
@@ -87,6 +87,22 @@ export async function findXctestrunPaths(testProductsPath: string): Promise<stri
   await collectXctestrunPaths(testProductsPath, paths);
   return paths.sort((left, right) => left.localeCompare(right));
 }
+export async function hasMultipleSimulatorPlatforms(testProductsPath: string): Promise<boolean> {
+  const xctestrunPaths = await findXctestrunPaths(testProductsPath);
+  const simulatorPlatforms = new Set<string>();
+
+  for (const xctestrunPath of xctestrunPaths) {
+    const contents = await fs.promises.readFile(xctestrunPath, 'utf8');
+    for (const match of contents.matchAll(/(?:^|[-/])([A-Za-z]+simulator)(?:[/\\])/gu)) {
+      simulatorPlatforms.add(match[1]!.toLowerCase());
+    }
+    if (simulatorPlatforms.size > 1) {
+      return true;
+    }
+  }
+
+  return false;
+}
 
 export function markTestProductsPathCompleted(testProductsPath: string | undefined): void {
   if (!testProductsPath) {