diff --git a/test/Printers.cpp b/test/Printers.cpp
index adf59f82..fc82357e 100644
--- a/test/Printers.cpp
+++ b/test/Printers.cpp
@@ -6,7 +6,7 @@
 
 #include "Printers.hpp"
 
-std::ostream& operator<<(std::ostream& os, const ArduinoJson::JsonValue& v) {
+std::ostream& operator<<(std::ostream& os, const ArduinoJson::JsonValue&) {
   os << "JsonValue";  // TODO
   return os;
 }
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