https://bugs.gentoo.org/920460
--- a/drivers/firebird/dbd_firebird.c
+++ b/drivers/firebird/dbd_firebird.c
@@ -43,6 +43,7 @@
 #include <string.h>
 #include <time.h>
 #include <ibase.h>
+#include <ctype.h>
 
 #include "dbd_firebird.h"
 #include "firebird_charsets.h"