diff --git a/src/serial.cc b/src/serial.cc
index a9e6f84b..31e72a5a 100755
--- a/src/serial.cc
+++ b/src/serial.cc
@@ -5,7 +5,7 @@
 # include <alloca.h>
 #endif
 
-#if defined (__MINGW32__)
+#if defined (__MINGW32__) && !defined(alloca)
 # define alloca __builtin_alloca
 #endif