diff --git a/libs/ssl/threading_alt.h b/libs/ssl/threading_alt.h
index 1105fb053..eacb0e0f0 100644
--- a/libs/ssl/threading_alt.h
+++ b/libs/ssl/threading_alt.h
@@ -1,4 +1,6 @@
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 
 typedef struct