diff --git a/tests/src/unit-regression2.cpp b/tests/src/unit-regression2.cpp
index f60b4a277..e6bc34cbf 100644
--- a/tests/src/unit-regression2.cpp
+++ b/tests/src/unit-regression2.cpp
@@ -66,6 +66,14 @@ using ordered_json = nlohmann::ordered_json;
     #endif
 #endif
 
+/////////////////////////////////////////////////////////////////////
+// for #4825 - explicitly instantiating basic_json must compile; this
+// forces instantiation of binary_writer::write_bjdata_ndarray, whose
+// static_cast<string_t> was ambiguous under explicit instantiation on
+// C++17. Merely compiling this translation unit is the regression test.
+/////////////////////////////////////////////////////////////////////
+template class nlohmann::basic_json<>;
+
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
 DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")