diff --git a/src/mfm_dup.cpp b/src/mfm_dup.cpp
index 9bd2780a..97eeecf3 100644
--- a/src/mfm_dup.cpp
+++ b/src/mfm_dup.cpp
@@ -50,4 +50,6 @@ mfm::dup(const Opts::Dup &opts_)
           throw std::runtime_error("invalid file type");
         }
     }
+
+  return 0;
 }