diff --git a/auparse/interpret.c b/auparse/interpret.c
index ad949c90f..5c182ae69 100644
--- a/auparse/interpret.c
+++ b/auparse/interpret.c
@@ -331,7 +331,7 @@ static void key_escape(const char *orig, char *dest, auparse_esc_t escape_mode)
 static int is_hex_string(const char *str)
 {
 	while (*str) {
-		if (!isdigit((unsigned char)*str))
+		if (!isxdigit((unsigned char)*str))
 			return 0;
 		str++;
 	}