isl_arg.h: add missing include

diff --git a/include/isl_arg.h b/include/isl_arg.h
index d8e038e..86ff19e 100644 (file)
--- a/include/isl_arg.h
+++ b/include/isl_arg.h
@@ -11,6 +11,7 @@
 #define ISL_ARG_H
 
 #include <stddef.h>
+#include <stdlib.h>
 
 #if defined(__cplusplus)
 extern "C" {