diff --git a/lib/chibi/ast.c b/lib/chibi/ast.c
index edf62989..9192df4f 100644
--- a/lib/chibi/ast.c
+++ b/lib/chibi/ast.c
@@ -5,6 +5,7 @@
 #include <chibi/eval.h>
 
 #ifndef PLAN9
+#include <stdlib.h>
 #include <errno.h>
 #endif