diff --git a/slre.c b/slre.c
index 5c0d33c..990a744 100644
--- a/slre.c
+++ b/slre.c
@@ -25,9 +25,12 @@
 
 #define MAX_BRANCHES 100
 #define MAX_BRACKETS 100
-#define ARRAY_SIZE(ar) (int) (sizeof(ar) / sizeof((ar)[0]))
 #define FAIL_IF(condition, error_code) if (condition) return (error_code)
 
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(ar) (int) (sizeof(ar) / sizeof((ar)[0]))
+#endif
+
 #ifdef SLRE_DEBUG
 #define DBG(x) printf x
 #else