diff --git a/include/spdlog/tweakme.h b/include/spdlog/tweakme.h
index 24361f30..6b4fc14c 100644
--- a/include/spdlog/tweakme.h
+++ b/include/spdlog/tweakme.h
@@ -71,7 +71,9 @@
 // In this case spdlog will try to include <fmt/format.h> so set your -I flag
 // accordingly.
 //
-// #define SPDLOG_FMT_EXTERNAL
+#ifndef SPDLOG_FMT_EXTERNAL
+#define SPDLOG_FMT_EXTERNAL
+#endif
 ///////////////////////////////////////////////////////////////////////////////
 
 ///////////////////////////////////////////////////////////////////////////////