diff --git a/test/src/unit-regression.cpp b/test/src/unit-regression.cpp
index f49c7caa7..8f011e02e 100644
--- a/test/src/unit-regression.cpp
+++ b/test/src/unit-regression.cpp
@@ -1493,7 +1493,7 @@ TEST_CASE("regression tests")
     )";
 
         // define parser callback
-        json::parser_callback_t cb = [](int depth, json::parse_event_t event, json & parsed)
+        json::parser_callback_t cb = [](int /*depth*/, json::parse_event_t event, json & parsed)
         {
             // skip object elements with key "Thumbnail"
             if (event == json::parse_event_t::key and parsed == json("Thumbnail"))