diff --git a/src/metric.cpp b/src/metric.cpp
index d8241b9..582e506 100644
--- a/src/metric.cpp
+++ b/src/metric.cpp
@@ -107,7 +107,8 @@
 class Metric::DataStartup : public Metric::CollectionData
 {
   public:
-    DataStartup(std::shared_ptr<details::CollectionFunction> function) :
+    explicit DataStartup(
+        std::shared_ptr<details::CollectionFunction> function) :
         function(std::move(function))
     {}