diff --git a/tools/c-arcmt-test/c-arcmt-test.c b/tools/c-arcmt-test/c-arcmt-test.c
index 86992da76b..19f6b8f30c 100644
--- a/tools/c-arcmt-test/c-arcmt-test.c
+++ b/tools/c-arcmt-test/c-arcmt-test.c
@@ -70,7 +70,12 @@ void thread_runner(void *client_data_v) {
 int main(int argc, const char **argv) {
   thread_info client_data;
 
+#if defined(_WIN32)
+  if (getenv("LIBCLANG_LOGGING") == NULL)
+    putenv("LIBCLANG_LOGGING=1");
+#else
   setenv("LIBCLANG_LOGGING", "1", /*overwrite=*/0);
+#endif
 
   if (getenv("CINDEXTEST_NOTHREADS"))
     return carcmttest_main(argc, argv);