diff --git a/src/propertywatch.hpp b/src/propertywatch.hpp
index 1d88eae..6cb1d63 100644
--- a/src/propertywatch.hpp
+++ b/src/propertywatch.hpp
@@ -130,9 +130,9 @@
                                          &callback),
         filterOps(filterOps)
     {}
-    PropertyWatchOfType(const PropertyIndex& watchIndex,
-                        bool ignoreStartCallback = false,
-                        Filters* filterOps = nullptr) :
+    explicit PropertyWatchOfType(const PropertyIndex& watchIndex,
+                                 bool ignoreStartCallback = false,
+                                 Filters* filterOps = nullptr) :
         PropertyWatch<DBusInterfaceType>(watchIndex, ignoreStartCallback,
                                          nullptr),
         filterOps(filterOps)