diff --git a/src/core/ffi.c b/src/core/ffi.c
index 8b5481cb..4949f9e6 100644
--- a/src/core/ffi.c
+++ b/src/core/ffi.c
@@ -30,6 +30,8 @@
 
 #ifdef _MSC_VER
 #define alloca _alloca
+#else
+#include <alloca.h>
 #endif
 
 #define JANET_FFI_MAX_RECUR 64