diff --git a/include/libultra/xprintf.h b/include/libultra/xprintf.h
index 400dc172..3b464dbe 100644
--- a/include/libultra/xprintf.h
+++ b/include/libultra/xprintf.h
@@ -8,7 +8,7 @@
 extern "C"{
 #endif
 
-extern int _Printf(void* (*prout_func)(void*, const char*, int), char* buf, const char* fmt, va_list ap);
+extern int _Printf(void* (*prout_func)(void*, const char*, int), void* arg, const char* fmt, va_list ap);
 
 #ifdef __cplusplus
 }
diff --git a/src/libultra/xprint.c b/src/libultra/xprint.c
index de0110d3..579ecbf1 100644
--- a/src/libultra/xprint.c
+++ b/src/libultra/xprint.c
@@ -1,5 +1,5 @@
 #include "libultra/xprintf.h"
 
-extern int _Printf(void* (*prout_func)(void*, const char*, int), char* buf, const char* fmt, va_list ap) {
+extern int _Printf(void* (*prout_func)(void*, const char*, int), void* arg, const char* fmt, va_list ap) {
 
 }