diff --git a/fdbmonitor/fdbmonitor.cpp b/fdbmonitor/fdbmonitor.cpp
index e0ea1e5e0d..a0d1be31f0 100644
--- a/fdbmonitor/fdbmonitor.cpp
+++ b/fdbmonitor/fdbmonitor.cpp
@@ -39,6 +39,7 @@
 
 #ifdef __FreeBSD__
 #include <sys/event.h>
+#define O_EVTONLY O_RDONLY
 #endif
 
 #ifdef __APPLE__