diff --git a/basis/core-foundation/fsevents/fsevents.factor b/basis/core-foundation/fsevents/fsevents.factor
index cbd2fca5e4..da45e0cde2 100644
--- a/basis/core-foundation/fsevents/fsevents.factor
+++ b/basis/core-foundation/fsevents/fsevents.factor
@@ -27,7 +27,7 @@ CONSTANT: kFSEventStreamEventFlagUnmount 128
 
 TYPEDEF: int FSEventStreamCreateFlags
 TYPEDEF: int FSEventStreamEventFlags
-TYPEDEF: longlong FSEventStreamEventId
+TYPEDEF: ulonglong FSEventStreamEventId
 TYPEDEF: void* FSEventStreamRef
 
 STRUCT: FSEventStreamContext