diff --git a/c/srfi/srfi-27.c b/c/srfi/srfi-27.c
index f864672..2e5eab5 100644
--- a/c/srfi/srfi-27.c
+++ b/c/srfi/srfi-27.c
@@ -36,6 +36,9 @@
 #include "scheme48.h" /* $SCHEME48/c/scheme48.h */
 #include <sys/time.h>
 
+#ifndef NULL
+  #define NULL 0
+#endif
 /* maximum value for random_integer: min(S48_MAX_FIXNUM_VALUE, m1) */
 #define m_max (((long)1 << 29) - 1)