diff --git a/aos/realtime_test.cc b/aos/realtime_test.cc
index 348489b..9a0c94e 100644
--- a/aos/realtime_test.cc
+++ b/aos/realtime_test.cc
@@ -132,6 +132,20 @@
 
 #endif
 
+// Tests that we see which CPUs we tried to set when it fails. This can be
+// useful for debugging.
+TEST(RealtimeDeathTest, SetAffinityErrorMessage) {
+  EXPECT_DEATH({ SetCurrentThreadAffinity(MakeCpusetFromCpus({1000})); },
+               "sched_setaffinity\\(0, sizeof\\(cpuset\\), &cpuset\\) == 0 "
+               "\\{CPUs 1000\\}: Invalid argument");
+  EXPECT_DEATH(
+      {
+        SetCurrentThreadAffinity(MakeCpusetFromCpus({1000, 1001}));
+      },
+      "sched_setaffinity\\(0, sizeof\\(cpuset\\), &cpuset\\) == 0 "
+      "\\{CPUs 1000, 1001\\}: Invalid argument");
+}
+
 }  // namespace aos::testing
 
 // We need a special gtest main to force die_on_malloc support on.  Otherwise