diff --git a/src/option_parser.cpp b/src/option_parser.cpp
index 484d0141..a4922c8c 100644
--- a/src/option_parser.cpp
+++ b/src/option_parser.cpp
@@ -48,6 +48,7 @@
 
 enum
   {
+    MERGERFS_OPT_DEBUG,
     MERGERFS_OPT_HELP,
     MERGERFS_OPT_VERSION
   };