diff --git a/io_internal.h b/io_internal.h
index 30d72ae..90def97 100644
--- a/io_internal.h
+++ b/io_internal.h
@@ -57,6 +57,7 @@ typedef struct {
 #endif
   long next_read;
   long next_write;
+  long next_defer;
   void* cookie;
   void* mmapped;
   long maplen;