diff --git a/compiler-rt/test/sanitizer_common/TestCases/Linux/pthread_getaffinity_np.cpp b/compiler-rt/test/sanitizer_common/TestCases/Linux/pthread_getaffinity_np.cpp
--- a/compiler-rt/test/sanitizer_common/TestCases/Linux/pthread_getaffinity_np.cpp
+++ b/compiler-rt/test/sanitizer_common/TestCases/Linux/pthread_getaffinity_np.cpp
@@ -5,6 +5,10 @@
 // sched_getaffinity).
 // UNSUPPORTED: android
 
+#ifndef _GNU_SOURCE
+#  define _GNU_SOURCE
+#endif
+
 #include <assert.h>
 #include <pthread.h>
 #include <stdio.h>
@@ -14,9 +18,13 @@
 
 int main() {
   cpu_set_t set_x;
-  int res = pthread_getaffinity_np(pthread_self(), sizeof(set_x), &set_x);
-  if (res != 0)
+  pthread_t tid = pthread_self();
+  int res = pthread_getaffinity_np(tid, sizeof(set_x), &set_x);
+  if (res != 0) {
+    fprintf(stderr, "tid: %lu\n", tid);
+    fprintf(stderr, "sizeof(set_x): %d\n", sizeof(set_x));
     fprintf(stderr, "res: %d\n", res);
+  }
   assert(res == 0);
   assert(CPU_COUNT_S(sizeof(set_x), &set_x) == get_nprocs());