diff --git a/src/common.c b/src/common.c
index 73cf24d..52f917f 100644
--- a/src/common.c
+++ b/src/common.c
@@ -111,3 +111,20 @@ read_password(char *buf, size_t len)
 	strncpy(buf, pwd, len);
 	buf[len-1] = '\0';
 }
+
+int
+check_topdomain(char *str)
+{
+       int i;
+
+       if(str[0] == '.') /* special case */
+               return 1;
+
+       for( i = 0; i < strlen(str); i++) {
+               if( isalpha(str[i]) || isdigit(str[i]) || str[i] == '-' || str[i] == '.' )
+                       continue;
+               else 
+		       return 1;
+       }
+       return 0;
+}
diff --git a/src/common.h b/src/common.h
index e6100ab..eb6f719 100644
--- a/src/common.h
+++ b/src/common.h
@@ -46,4 +46,6 @@ void do_detach();
 
 void read_password(char*, size_t);
 
+int check_topdomain(char *);
+
 #endif
diff --git a/src/iodine.c b/src/iodine.c
index 4dc6217..5b23c83 100644
--- a/src/iodine.c
+++ b/src/iodine.c
@@ -697,8 +697,13 @@ main(int argc, char **argv)
 
 	set_nameserver(nameserv_addr);
 
-	if (strlen(topdomain) > 128 || topdomain[0] == '.') {
-		warnx("Use a topdomain max 128 chars long. Do not start it with a dot.\n");
+	if(strlen(topdomain) <= 128) {
+		if(check_topdomain(topdomain)) {
+			warnx("Topdomain contains invalid characters.\n");
+			usage();
+		}
+	} else {
+		warnx("Use a topdomain max 128 chars long.\n");
 		usage();
 	}
 
diff --git a/src/iodined.c b/src/iodined.c
index ad70777..0d4694d 100644
--- a/src/iodined.c
+++ b/src/iodined.c
@@ -526,8 +526,13 @@ main(int argc, char **argv)
 		usage();
 
 	topdomain = strdup(argv[1]);
-	if (strlen(topdomain) > 128 || topdomain[0] == '.') {
-		warnx("Use a topdomain max 128 chars long. Do not start it with a dot.\n");
+	if(strlen(topdomain) <= 128) {
+		if(check_topdomain(topdomain)) {
+			warnx("Topdomain contains invalid characters.\n");
+			usage();
+		}
+	} else {
+		warnx("Use a topdomain max 128 chars long.\n");
 		usage();
 	}