diff --git a/abstract-machine/klib/src/printf.c b/abstract-machine/klib/src/printf.c
index 88847a0..40764f1 100644
--- a/abstract-machine/klib/src/printf.c
+++ b/abstract-machine/klib/src/printf.c
@@ -59,6 +59,7 @@ static inline int print_fmt(char **out, int n, const char** fmt, void* _ap) {
             break;
     }
     (*fmt) ++;
+    *(va_list*)_ap = ap;
     return ret;
 }