diff --git a/include/lib/libc/stdio.h b/include/lib/libc/stdio.h
index 2d9e655..ba13683 100644
--- a/include/lib/libc/stdio.h
+++ b/include/lib/libc/stdio.h
@@ -22,6 +22,7 @@
 
 #ifdef STDARG_H
 int vprintf(const char *fmt, va_list args);
+int vsnprintf(char *s, size_t n, const char *fmt, va_list args);
 #endif
 
 int putchar(int c);