diff --git a/tests/src/unit-conversions.cpp b/tests/src/unit-conversions.cpp
index 81b8608fb8..d63f8521e8 100644
--- a/tests/src/unit-conversions.cpp
+++ b/tests/src/unit-conversions.cpp
@@ -1683,7 +1683,7 @@ TEST_CASE("std::filesystem::path")
 }
 #endif
 
-#ifndef JSON_USE_IMPLICIT_CONVERSIONS
+#if !JSON_USE_IMPLICIT_CONVERSIONS
 TEST_CASE("std::optional")
 {
     SECTION("null")