diff --git a/include/instance.hpp b/include/instance.hpp
index a7feb78..8f17525 100644
--- a/include/instance.hpp
+++ b/include/instance.hpp
@@ -226,7 +226,7 @@ public:
     class ObtainToken : public CURLWrapper
     {
     public:
-        ObtainToken(Instance &instance)
+        explicit ObtainToken(Instance &instance)
             : _instance{instance}
             , _baseuri{instance.get_baseuri()}
         {