--- a/js/src/shell/OSObject.cpp
+++ b/js/src/shell/OSObject.cpp
@@ -32,17 +32,19 @@
 #include "js/Conversions.h"
 #include "shell/jsshell.h"
 #include "vm/StringBuffer.h"
 #include "vm/TypedArrayObject.h"
 
 #include "jsobjinlines.h"
 
 #ifdef XP_WIN
-# define PATH_MAX (MAX_PATH > _MAX_DIR ? MAX_PATH : _MAX_DIR)
+# ifndef PATH_MAX
+#  define PATH_MAX (MAX_PATH > _MAX_DIR ? MAX_PATH : _MAX_DIR)
+# endif
 # define getcwd _getcwd
 #else
 # include <libgen.h>
 #endif
 
 using js::shell::RCFile;
 
 namespace js {