diff --git a/libcxx/test/support/platform_support.h b/libcxx/test/support/platform_support.h
--- a/libcxx/test/support/platform_support.h
+++ b/libcxx/test/support/platform_support.h
@@ -55,6 +55,9 @@
 #if defined(_WIN32)
     char Name[] = "libcxx.XXXXXX";
     if (_mktemp_s(Name, sizeof(Name)) != 0) abort();
+    FILE *File = fopen(Name, "wb");
+    if (File)
+        fclose(File);
     return Name;
 #else
     std::string Name;