diff --git a/tests/ffi/tests.cc b/tests/ffi/tests.cc
index dffc40540..893bc1051 100644
--- a/tests/ffi/tests.cc
+++ b/tests/ffi/tests.cc
@@ -14,6 +14,8 @@ extern "C" void cxx_test_suite_set_correct() noexcept;
 extern "C" tests::R *cxx_test_suite_get_box() noexcept;
 extern "C" bool cxx_test_suite_r_is_correct(const tests::R *) noexcept;
 
+bool PmrDeleterForC_callback_used{false};
+
 namespace tests {
 
 #if __cplusplus < 201703L
@@ -139,8 +141,6 @@ std::unique_ptr<C> c_return_unique_ptr() {
   return std::unique_ptr<C>(new C{2020});
 }
 
-extern "C" bool PmrDeleterForC_callback_used{false};
-
 void PmrDeleterForC::operator()(C* obj) {
     alloc.destroy(obj);
     alloc.deallocate(obj, 1);