diff --git a/include/libtorrent/alloca.hpp b/include/libtorrent/alloca.hpp
index 2d2601e7b..71b87f9db 100644
--- a/include/libtorrent/alloca.hpp
+++ b/include/libtorrent/alloca.hpp
@@ -37,12 +37,12 @@ POSSIBILITY OF SUCH DAMAGE.
 #ifdef TORRENT_WINDOWS
 
 #include <malloc.h>
-#define TORRENT_ALLOCA(t, n) static_cast<t*>(_alloca(sizeof(t) * n));
+#define TORRENT_ALLOCA(t, n) static_cast<t*>(_alloca(sizeof(t) * (n)));
 
 #else
 
 #include <alloca.h>
-#define TORRENT_ALLOCA(t, n) static_cast<t*>(alloca(sizeof(t) * n));
+#define TORRENT_ALLOCA(t, n) static_cast<t*>(alloca(sizeof(t) * (n)));
 
 #endif