diff --git a/src/iodine.c b/src/iodine.c
index 7e21e41..904ee0c 100644
--- a/src/iodine.c
+++ b/src/iodine.c
@@ -582,6 +582,10 @@ main(int argc, char **argv)
 		usage();
 
 	topdomain = strdup(argv[1]);
+	if (strlen(topdomain) > 128 || topdomain[0] == '.') {
+		printf("Use a topdomain max 128 chars long. Do not start it with a dot.\n");
+		usage();
+	}
 
 	if(username) {
 		pw = getpwnam(username);
diff --git a/src/iodined.c b/src/iodined.c
index dd590fd..5ab7242 100644
--- a/src/iodined.c
+++ b/src/iodined.c
@@ -521,6 +521,10 @@ main(int argc, char **argv)
 		usage();
 
 	topdomain = strdup(argv[1]);
+	if (strlen(topdomain) > 128 || topdomain[0] == '.') {
+		printf("Use a topdomain max 128 chars long. Do not start it with a dot.\n");
+		usage();
+	}
 
 	if (username) {
 		pw = getpwnam(username);