diff --git a/lib/exprengine.h b/lib/exprengine.h
index d14c0f5ba..344bc93b1 100644
--- a/lib/exprengine.h
+++ b/lib/exprengine.h
@@ -315,7 +315,7 @@ namespace ExprEngine {
 
     class FunctionCallArgumentValues: public Value {
     public:
-        FunctionCallArgumentValues(const std::vector<ExprEngine::ValuePtr> &argValues)
+        explicit FunctionCallArgumentValues(const std::vector<ExprEngine::ValuePtr> &argValues)
             : Value("argValues", ValueType::FunctionCallArgumentValues)
             , argValues(argValues)
         {}