diff --git a/src/state.hpp b/src/state.hpp
index 5f36db48..67e98fdb 100644
--- a/src/state.hpp
+++ b/src/state.hpp
@@ -102,7 +102,7 @@ public:
     {
     }
 
-    int ref_count;
+    std::atomic<u32> ref_count;
     int backing_id;
     FileInfo *fi;
   };