diff --git a/compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py b/compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py
--- a/compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py
+++ b/compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py
@@ -2,4 +2,13 @@
 
 import os, sys, subprocess, json
 
+
+device_id = os.environ.get('SANITIZER_IOSSIM_TEST_DEVICE_IDENTIFIER')
+if not device_id:
+    raise EnvironmentError('Specify SANITIZER_IOSSIM_TEST_DEVICE_IDENTIFIER to select which simulator to use.')
+
+boot_cmd = ['xcrun', 'simctl', 'bootstatus', device_id, '-b']
+subprocess.check_call(boot_cmd)
+
+
 print(json.dumps({"env": {}}))