diff --git a/folly/portability/Unistd.h b/folly/portability/Unistd.h
index 2262210a12e..1b8dd7484fe 100644
--- a/folly/portability/Unistd.h
+++ b/folly/portability/Unistd.h
@@ -21,7 +21,7 @@
 #include <unistd.h>
 
 #if defined(__APPLE__) || defined(__EMSCRIPTEN__)
-using off64_t = off_t;
+typedef off_t off64_t;
 
 off64_t lseek64(int fh, off64_t off, int orig);