diff --git a/projects/h2o/h2o-fuzzer-http1.options b/projects/h2o/h2o-fuzzer-http1.options
index 907ae122f..97ff13ba7 100644
--- a/projects/h2o/h2o-fuzzer-http1.options
+++ b/projects/h2o/h2o-fuzzer-http1.options
@@ -1,3 +1,4 @@
 [libfuzzer]
+close_fd_mask = 3
 max_len = 16384
 dict = http.dict