diff --git a/runtime/gc/allocator/rosalloc.cc b/runtime/gc/allocator/rosalloc.cc
index 656c55b..09fb97a 100644
--- a/runtime/gc/allocator/rosalloc.cc
+++ b/runtime/gc/allocator/rosalloc.cc
@@ -529,7 +529,7 @@
 }
 
 size_t RosAlloc::Free(Thread* self, void* ptr) {
-  WriterMutexLock rmu(self, bulk_free_lock_);
+  ReaderMutexLock rmu(self, bulk_free_lock_);
   return FreeInternal(self, ptr);
 }