diff --git a/libpsx/include/stdio.h b/libpsx/include/stdio.h
index 0ea5828..a790aab 100644
--- a/libpsx/include/stdio.h
+++ b/libpsx/include/stdio.h
@@ -104,7 +104,7 @@ int vsnprintf(char *string, size_t size, const char *fmt, va_list ap);
 int vsprintf(char *string, const char *fmt, va_list ap);
 int sprintf(char *string, const char *fmt, ...);
 int snprintf(char *string, size_t size, const char *fmt, ...);
-int vprintf(char *fmt, va_list ap);
+int vprintf(const char *fmt, va_list ap);
 
 FILE *fdopen(int fildes, const char *mode);
 FILE *fopen(const char *path, const char *mode);
diff --git a/libpsx/src/libc/printf.c b/libpsx/src/libc/printf.c
index ce8ffcd..a278435 100644
--- a/libpsx/src/libc/printf.c
+++ b/libpsx/src/libc/printf.c
@@ -843,7 +843,7 @@ static int out_put_in_string(char *string, unsigned int sz, char c, int pos)
 	return 1;
 }
 
-int vprintf(char *fmt, va_list ap)
+int vprintf(const char *fmt, va_list ap)
 {
 	return __vsnprintf_internal(NULL, -1, fmt, ap, out_put_in_string);
 }