https://bugs.gentoo.org/871705
--- a/src/snprintf.c
+++ b/src/snprintf.c
@@ -2,6 +2,11 @@
 # include <config.h>
 #endif
 
+#include <ctype.h>
+#include <stddef.h>
+#include <string.h>
+#include <stdio.h>
+
 #include <errno.h>
 #if defined(HAVE_STDARG_H) && (HAVE_STDARG_H != 0)
 # include <stdarg.h>