diff --git a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
index d06d1784..03b7c86b 100644
--- a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
+++ b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
@@ -64,7 +64,11 @@ BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer, ULONG RandomBufferLength);
 #endif
 
 #ifndef TLS
-# define TLS
+# ifdef _WIN32
+#  define TLS __declspec(thread)
+# else
+#  define TLS
+# endif
 #endif
 
 typedef struct Salsa20RandomGlobal_ {