diff --git a/src/common.c b/src/common.c
index b4772bb..b15fb7a 100644
--- a/src/common.c
+++ b/src/common.c
@@ -324,34 +324,62 @@ read_password(char *buf, size_t len)
 }
 
 int
-check_topdomain(char *str)
+check_topdomain(char *str, char **errormsg)
 {
 	int i;
 	int dots = 0;
 	int chunklen = 0;
 
-	if (strlen(str) < 3)
+	if (strlen(str) < 3) {
+		if (errormsg) *errormsg = "Too short (< 3)";
 		return 1;
-	if (strlen(str) > 128)
+	}
+	if (strlen(str) > 128) {
+		if (errormsg) *errormsg = "Too long (> 128)";
 		return 1;
+	}
+
+	if (str[0] == '.') {
+		if (errormsg) *errormsg = "Starts with a dot";
+		return 1;
+	}
 
 	for( i = 0; i < strlen(str); i++) {
 		if(str[i] == '.') {
 			dots++;
-			/* This will also catch the case where topdomain starts with a dot */
-			if (chunklen == 0 || chunklen > 63)
+			if (chunklen == 0) {
+				if (errormsg) *errormsg = "Consecutive dots";
 				return 1;
+			}
+			if (chunklen > 63) {
+				if (errormsg) *errormsg = "Too long domain part (> 63)";
+				return 1;
+			}
 			chunklen = 0;
-		} else
+		} else {
 			chunklen++;
-		if( isalpha(str[i]) || isdigit(str[i]) || str[i] == '-' || str[i] == '.' )
+		}
+		if( (str[i] >= 'a' && str[i] <= 'z') || (str[i] >= 'A' && str[i] <= 'Z') || 
+				isdigit(str[i]) || str[i] == '-' || str[i] == '.' ) {
 			continue;
-		else
+		} else {
+			if (errormsg) *errormsg = "Contains illegal character (allowed: [a-zA-Z0-9-.])";
 			return 1;
+		}
 	}
 
-	if (chunklen == 0 || chunklen > 63 || dots == 0)
+	if (dots == 0) {
+		if (errormsg) *errormsg = "No dots";
 		return 1;
+	}
+	if (chunklen == 0) {
+		if (errormsg) *errormsg = "Ends with a dot";
+		return 1;
+	}
+	if (chunklen > 63) {
+		if (errormsg) *errormsg = "Too long domain part (> 63)";
+		return 1;
+	}
 
 	return 0;
 }
diff --git a/src/common.h b/src/common.h
index bbadc9f..534996c 100644
--- a/src/common.h
+++ b/src/common.h
@@ -120,7 +120,7 @@ void do_pidfile(char *);
 
 void read_password(char*, size_t);
 
-int check_topdomain(char *);
+int check_topdomain(char *, char **);
 
 #if defined(WINDOWS32) || defined(ANDROID)
 #ifndef ANDROID
diff --git a/src/iodine.c b/src/iodine.c
index 0975739..e53ae37 100644
--- a/src/iodine.c
+++ b/src/iodine.c
@@ -120,6 +120,7 @@ main(int argc, char **argv)
 {
 	char *nameserv_host;
 	char *topdomain;
+	char *errormsg;
 #ifndef WINDOWS32
 	struct passwd *pw;
 #endif
@@ -149,6 +150,7 @@ main(int argc, char **argv)
 
 	nameserv_host = NULL;
 	topdomain = NULL;
+	errormsg = NULL;
 #ifndef WINDOWS32
 	pw = NULL;
 #endif
@@ -309,14 +311,8 @@ main(int argc, char **argv)
 		/* NOTREACHED */
 	}	
 
-	if (strlen(topdomain) <= 128) {
-		if(check_topdomain(topdomain)) {
-			warnx("Topdomain contains invalid characters.\n");
-			usage();
-			/* NOTREACHED */
-		}
-	} else {
-		warnx("Use a topdomain max 128 chars long.\n");
+	if(check_topdomain(topdomain, &errormsg)) {
+		warnx("Invalid topdomain: %s", errormsg);
 		usage();
 		/* NOTREACHED */
 	}
diff --git a/src/iodined.c b/src/iodined.c
index 6ebf3a6..ef6c163 100644
--- a/src/iodined.c
+++ b/src/iodined.c
@@ -2233,6 +2233,7 @@ main(int argc, char **argv)
 {
 	extern char *__progname;
 	char *listen_ip;
+	char *errormsg;
 #ifndef WINDOWS32
 	struct passwd *pw;
 #endif
@@ -2267,6 +2268,7 @@ main(int argc, char **argv)
 #ifndef WINDOWS32
 	pw = NULL;
 #endif
+	errormsg = NULL;
 	username = NULL;
 	newroot = NULL;
 	context = NULL;
@@ -2403,14 +2405,10 @@ main(int argc, char **argv)
 	}
 
 	topdomain = strdup(argv[1]);
-	if (strlen(topdomain) <= 128) {
-		if(check_topdomain(topdomain)) {
-			warnx("Topdomain contains invalid characters.");
-			usage();
-		}
-	} else {
-		warnx("Use a topdomain max 128 chars long.");
+	if(check_topdomain(topdomain, &errormsg)) {
+		warnx("Invalid topdomain: %s", errormsg);
 		usage();
+		/* NOTREACHED */
 	}
 
 	if (username != NULL) {
diff --git a/tests/common.c b/tests/common.c
index 9c84e4a..c1bc73f 100644
--- a/tests/common.c
+++ b/tests/common.c
@@ -6,60 +6,85 @@
 
 START_TEST(test_topdomain_ok)
 {
-	fail_if(check_topdomain("foo.0123456789.qwertyuiop.asdfghjkl.zxcvbnm.com"));
+	char *error;
+
+	fail_if(check_topdomain("foo.0123456789.qwertyuiop.asdfghjkl.zxcvbnm.com", &error));
 
 	/* Not allowed to start with dot */
-	fail_unless(check_topdomain(".foo.0123456789.qwertyuiop.asdfghjkl.zxcvbnm.com"));
+	fail_unless(check_topdomain(".foo.0123456789.qwertyuiop.asdfghjkl.zxcvbnm.com", &error));
+	fail_if(strcmp("Starts with a dot", error));
+
+	/* Test missing error msg ptr */
+	fail_unless(check_topdomain(".foo", NULL));
 }
 END_TEST
 
 START_TEST(test_topdomain_length)
 {
+	char *error;
+
 	/* Test empty and too short */
-	fail_unless(check_topdomain(""));
-	fail_unless(check_topdomain("a"));
-	fail_unless(check_topdomain(".a"));
-	fail_unless(check_topdomain("a."));
-	fail_unless(check_topdomain("ab"));
-	fail_if(check_topdomain("a.b"));
+	fail_unless(check_topdomain("", &error));
+	fail_if(strcmp("Too short (< 3)", error));
+	fail_unless(check_topdomain("a", &error));
+	fail_if(strcmp("Too short (< 3)", error));
+	fail_unless(check_topdomain(".a", &error));
+	fail_if(strcmp("Too short (< 3)", error));
+	fail_unless(check_topdomain("a.", &error));
+	fail_if(strcmp("Too short (< 3)", error));
+	fail_unless(check_topdomain("ab", &error));
+	fail_if(strcmp("Too short (< 3)", error));
+	fail_if(check_topdomain("a.b", &error));
+	fail_if(strcmp("Too short (< 3)", error));
 
 	/* Test too long (over 128, need rest of space for data) */
 	fail_unless(check_topdomain(
 		"abcd12345.abcd12345.abcd12345.abcd12345.abcd12345."
 		"abcd12345.abcd12345.abcd12345.abcd12345.abcd12345."
-		"abcd12345.abcd12345.foo129xxx"));
+		"abcd12345.abcd12345.foo129xxx", &error));
+	fail_if(strcmp("Too long (> 128)", error));
 	fail_if(check_topdomain(
 		"abcd12345.abcd12345.abcd12345.abcd12345.abcd12345."
 		"abcd12345.abcd12345.abcd12345.abcd12345.abcd12345."
-		"abcd12345.abcd12345.foo128xx"));
+		"abcd12345.abcd12345.foo128xx", &error));
 }
 END_TEST
 
 START_TEST(test_topdomain_chunks)
 {
+	char *error;
+
 	/* Must have at least one dot */
-	fail_if(check_topdomain("abcde.gh"));
-	fail_unless(check_topdomain("abcdefgh"));
+	fail_if(check_topdomain("abcde.gh", &error));
+	fail_unless(check_topdomain("abcdefgh", &error));
+	fail_if(strcmp("No dots", error));
 
 	/* Not two consecutive dots */
-	fail_unless(check_topdomain("abc..defgh"));
+	fail_unless(check_topdomain("abc..defgh", &error));
+	fail_if(strcmp("Consecutive dots", error));
 
 	/* Not end with a dots */
-	fail_unless(check_topdomain("abc.defgh."));
+	fail_unless(check_topdomain("abc.defgh.", &error));
+	fail_if(strcmp("Ends with a dot", error));
 
 	/* No chunk longer than 63 chars */
-	fail_unless(check_topdomain("123456789012345678901234567890"
-		"1234567890123456789012345678904444.com"));
 	fail_if(check_topdomain("123456789012345678901234567890"
-		"123456789012345678901234567890333.com"));
-	fail_unless(check_topdomain("abc.123456789012345678901234567890"
-		"1234567890123456789012345678904444.com"));
+		"123456789012345678901234567890333.com", &error));
+	fail_unless(check_topdomain("123456789012345678901234567890"
+		"1234567890123456789012345678904444.com", &error));
+	fail_if(strcmp("Too long domain part (> 63)", error));
+
 	fail_if(check_topdomain("abc.123456789012345678901234567890"
-		"123456789012345678901234567890333.com"));
+		"123456789012345678901234567890333.com", &error));
 	fail_unless(check_topdomain("abc.123456789012345678901234567890"
-		"1234567890123456789012345678904444"));
+		"1234567890123456789012345678904444.com", &error));
+	fail_if(strcmp("Too long domain part (> 63)", error));
+
 	fail_if(check_topdomain("abc.123456789012345678901234567890"
-		"123456789012345678901234567890333"));
+		"123456789012345678901234567890333", &error));
+	fail_unless(check_topdomain("abc.123456789012345678901234567890"
+		"1234567890123456789012345678904444", &error));
+	fail_if(strcmp("Too long domain part (> 63)", error));
 }
 END_TEST