Index: test/lit.common.cfg
===================================================================
--- test/lit.common.cfg
+++ test/lit.common.cfg
@@ -127,14 +127,18 @@
   ios_or_iossim = "iossim" if config.apple_platform.endswith("sim") else "ios"
 
   config.available_features.add('ios')
+  device_id_env = "SANITIZER_" + ios_or_iossim.upper() + "_TEST_DEVICE_IDENTIFIER"
   if ios_or_iossim == "iossim":
     config.available_features.add('iossim')
+    if device_id_env not in os.environ:
+      lit_config.fatal(
+        '{} must be set in the environment when running iossim tests'.format(
+          device_id_env))
   if config.apple_platform != "ios" and config.apple_platform != "iossim":
     config.available_features.add(config.apple_platform)
 
   ios_commands_dir = os.path.join(config.compiler_rt_src_root, "test", "sanitizer_common", "ios_commands")
 
-  device_id_env = "SANITIZER_" + ios_or_iossim.upper() + "_TEST_DEVICE_IDENTIFIER"
   run_wrapper = os.path.join(ios_commands_dir, ios_or_iossim + "_run.py")
   env_wrapper = os.path.join(ios_commands_dir, ios_or_iossim + "_env.py")
   compile_wrapper = os.path.join(ios_commands_dir, ios_or_iossim + "_compile.py")