diff --git a/basis/unix/ffi/bsd/macosx/macosx.factor b/basis/unix/ffi/bsd/macosx/macosx.factor
index a2e75b6ca6..a7c47f0ff8 100644
--- a/basis/unix/ffi/bsd/macosx/macosx.factor
+++ b/basis/unix/ffi/bsd/macosx/macosx.factor
@@ -32,7 +32,7 @@ STRUCT: utmpx
 
 CONSTANT: __DARWIN_MAXPATHLEN 1024
 CONSTANT: __DARWIN_MAXNAMELEN 255
-CONSTANT: __DARWIN_MAXNAMELEN+1 255
+CONSTANT: __DARWIN_MAXNAMELEN+1 256
 
 STRUCT: dirent
     { d_ino ino_t }