diff --git a/src/core/lib/support/cpu_posix.cc b/src/core/lib/support/cpu_posix.cc
index 503a96b4c8a..c32ca4659c7 100644
--- a/src/core/lib/support/cpu_posix.cc
+++ b/src/core/lib/support/cpu_posix.cc
@@ -18,19 +18,20 @@
 
 #include <grpc/support/port_platform.h>
 
-#ifdef GPR_CPU_POSIX
+#if defined(GPR_CPU_POSIX)
 
 #include <errno.h>
+#include <pthread.h>
 #include <string.h>
 #include <unistd.h>
 
+#include <atomic>
+
 #include <grpc/support/cpu.h>
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
 #include <grpc/support/useful.h>
 
-static __thread char magic_thread_local;
-
 static long ncpus = 0;
 
 static void init_ncpus() {
@@ -52,7 +53,27 @@ unsigned gpr_cpu_current_cpu(void) {
      most code that's using this is using it to shard across work queues though,
      so here we use thread identity instead to achieve a similar though not
      identical effect */
-  return (unsigned)GPR_HASH_POINTER(&magic_thread_local, gpr_cpu_num_cores());
+  static auto DeleteValue = [](void *value_ptr) {
+    unsigned int *value = static_cast<unsigned int *>(value_ptr);
+    if (value) {
+      delete value;
+    }
+  };
+  static pthread_key_t thread_id_key;
+  static int thread_id_key_create_result __attribute__((unused)) =
+      pthread_key_create(&thread_id_key, DeleteValue);
+  // pthread_t isn't portably defined to map to an integral type. So keep track
+  // of thread identity explicitly so hashing works reliably.
+  static std::atomic<unsigned int> thread_counter(0);
+
+  unsigned int *thread_id =
+      static_cast<unsigned int *>(pthread_getspecific(thread_id_key));
+  if (thread_id == nullptr) {
+    thread_id = new unsigned int(thread_counter++);
+    pthread_setspecific(thread_id_key, thread_id);
+  }
+
+  return (unsigned)GPR_HASH_POINTER(*thread_id, gpr_cpu_num_cores());
 }
 
 #endif /* GPR_CPU_POSIX */