diff --git a/src/mergerfs.cpp b/src/mergerfs.cpp
index 2c7cf24f..b09da662 100644
--- a/src/mergerfs.cpp
+++ b/src/mergerfs.cpp
@@ -406,6 +406,7 @@ main(int    argc_,
   app.add_option("branches",branches)
     ->delimiter(':')
     ->expected(1,-1)
+    ->required()
     ;
 
   app.add_option("mountpoint",mountpoint)