diff --git a/src/cli.cc b/src/cli.cc
index cf0f45f..54cea4a 100644
--- a/src/cli.cc
+++ b/src/cli.cc
@@ -56,6 +56,9 @@ static struct option getopt_options[] = {
 
 ot::status ot::parse_options(int argc, char** argv, ot::options& opt)
 {
+	static ot::encoding_converter to_utf8("", "UTF-8");
+	std::string utf8;
+	ot::status rc;
 	opt = {};
 	if (argc == 1)
 		return {st::bad_arguments, "No arguments specified. Use -h for help."};
@@ -81,17 +84,23 @@ ot::status ot::parse_options(int argc, char** argv, ot::options& opt)
 			opt.overwrite = true;
 			break;
 		case 'd':
-			if (strchr(optarg, '=') != nullptr)
+			rc = to_utf8(optarg, strlen(optarg), utf8);
+			if (rc != ot::st::ok)
+				return {st::bad_arguments, "Could not encode argument into UTF-8: " + rc.message};
+			if (strchr(utf8.c_str(), '=') != nullptr)
 				return {st::bad_arguments, "Invalid field name '"s + optarg + "'."};
-			opt.to_delete.emplace_back(optarg);
+			opt.to_delete.emplace_back(std::move(utf8));
 			break;
 		case 'a':
 		case 's':
-			if (strchr(optarg, '=') == NULL)
+			rc = to_utf8(optarg, strlen(optarg), utf8);
+			if (rc != ot::st::ok)
+				return {st::bad_arguments, "Could not encode argument into UTF-8: " + rc.message};
+			if (strchr(utf8.c_str(), '=') == NULL)
 				return {st::bad_arguments, "Invalid comment '"s + optarg + "'."};
-			opt.to_add.emplace_back(optarg);
 			if (c == 's')
-				opt.to_delete.emplace_back(optarg);
+				opt.to_delete.emplace_back(utf8);
+			opt.to_add.emplace_back(std::move(utf8));
 			break;
 		case 'S':
 			opt.set_all = true;
diff --git a/src/opustags.h b/src/opustags.h
index d9db029..94772f7 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -400,6 +400,8 @@ struct options {
 	 * #to_add takes precedence over #to_delete, so if the same comment appears in both lists,
 	 * the one in #to_delete applies only to the previously existing tags.
 	 *
+	 * The strings are stored in UTF-8.
+	 *
 	 * \todo Consider making it case-insensitive.
 	 * \todo Allow values like `ARTIST=x` to delete only the ARTIST comment whose value is x.
 	 *
@@ -416,6 +418,8 @@ struct options {
 	 * List of comments to add, in the current system encoding. For exemple `TITLE=a b c`. They
 	 * must be valid.
 	 *
+	 * The strings are stored in UTF-8.
+	 *
 	 * Options: --add, --set, --set-all
 	 */
 	std::vector<std::string> to_add;