Index: lib/sanitizer_common/sanitizer_coverage_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_coverage_libcdep.cc
+++ lib/sanitizer_common/sanitizer_coverage_libcdep.cc
@@ -226,7 +226,8 @@
   Enable();  // Make sure coverage is enabled at this point.
   s32 n = guards[0];
   for (s32 j = 1; j <= n; j++) {
-    uptr idx = atomic_fetch_add(&pc_array_index, 1, memory_order_relaxed);
+    uptr idx = atomic_load_relaxed(&pc_array_index);
+    atomic_store_relaxed(&pc_array_index, idx + 1);
     guards[j] = -static_cast<s32>(idx + 1);
   }
 }