diff --git a/src/Mass/Mass.h b/src/Mass/Mass.h
index eed4138..e05a47c 100644
--- a/src/Mass/Mass.h
+++ b/src/Mass/Mass.h
@@ -24,7 +24,7 @@ enum class MassState : std::uint8_t {
 
 class Mass {
     public:
-        Mass(const std::string& filename);
+        explicit Mass(const std::string& filename);
 
         Mass(const Mass&) = delete;
         Mass& operator=(const Mass&) = delete;