diff --git a/abstract-machine/klib/src/printf.c b/abstract-machine/klib/src/printf.c
index 788b916..88847a0 100644
--- a/abstract-machine/klib/src/printf.c
+++ b/abstract-machine/klib/src/printf.c
@@ -27,7 +27,8 @@ int num_to_ascii(int num, int power, int size, char *buf) {
     return ret;
 }
 
-static inline int print_fmt(char **out, int n, const char** fmt, va_list ap) {
+static inline int print_fmt(char **out, int n, const char** fmt, void* _ap) {
+    va_list ap = *(va_list*)_ap;
     int ret = 0;
     switch (**fmt) {
         case 'd':
@@ -67,7 +68,7 @@ int rvsnprintf(char* out, size_t n, const char* fmt, va_list ap) {
         if (*fmt == '%') {
             // FIXME
             fmt++;
-            print_fmt(&out, 123, &fmt, ap);
+            print_fmt(&out, 123, &fmt, &ap);
             continue;
         }
         *out = *fmt;