diff --git a/src/cli.cc b/src/cli.cc
index fd82b28..ea2a92b 100644
--- a/src/cli.cc
+++ b/src/cli.cc
@@ -58,6 +58,7 @@ ot::status ot::parse_options(int argc, char** argv, ot::options& opt)
 {
 	static ot::encoding_converter to_utf8("", "UTF-8");
 	std::string utf8;
+	std::string::size_type equal;
 	ot::status rc;
 	opt = {};
 	if (argc == 1)
@@ -96,10 +97,10 @@ ot::status ot::parse_options(int argc, char** argv, ot::options& opt)
 			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 + "'."};
+			if ((equal = utf8.find('=')) == std::string::npos)
+				return {st::bad_arguments, "Comment does not contain an equal sign: "s + optarg + "."};
 			if (c == 's')
-				opt.to_delete.emplace_back(utf8);
+				opt.to_delete.emplace_back(utf8.substr(0, equal));
 			opt.to_add.emplace_back(std::move(utf8));
 			break;
 		case 'S':
diff --git a/t/cli.cc b/t/cli.cc
index f8e0ddb..50713f7 100644
--- a/t/cli.cc
+++ b/t/cli.cc
@@ -52,7 +52,7 @@ void check_good_arguments()
 
 	opt = parse({"opustags", "x", "--output", "y", "-D", "-s", "X=Y Z"});
 	if (opt.path_in != "x" || opt.path_out != "y" || !opt.delete_all || opt.overwrite ||
-	    opt.to_delete.size() != 1 || opt.to_delete[0] != "X=Y Z" ||
+	    opt.to_delete.size() != 1 || opt.to_delete[0] != "X" ||
 	    opt.to_add.size() != 1 || opt.to_add[0] != "X=Y Z")
 		throw failure("unexpected option parsing result for case #1");
 
@@ -75,8 +75,8 @@ void check_bad_arguments()
 	error_case({"opustags"}, "No arguments specified. Use -h for help.", "no arguments");
 	error_case({"opustags", "--output", ""}, "Output file path cannot be empty.", "empty output path");
 	error_case({"opustags", "--delete", "X="}, "Invalid field name 'X='.", "bad field name for -d");
-	error_case({"opustags", "-a", "X"}, "Invalid comment 'X'.", "bad comment for -a");
-	error_case({"opustags", "--set", "X"}, "Invalid comment 'X'.", "bad comment for --set");
+	error_case({"opustags", "-a", "X"}, "Comment does not contain an equal sign: X.", "bad comment for -a");
+	error_case({"opustags", "--set", "X"}, "Comment does not contain an equal sign: X.", "bad comment for --set");
 	error_case({"opustags", "-a"}, "Missing value for option '-a'.", "short option with missing value");
 	error_case({"opustags", "--add"}, "Missing value for option '--add'.", "long option with missing value");
 	error_case({"opustags", "-x"}, "Unrecognized option '-x'.", "unrecognized short option");
diff --git a/t/opustags.t b/t/opustags.t
index 4e1942f..c8fe613 100755
--- a/t/opustags.t
+++ b/t/opustags.t
@@ -139,7 +139,7 @@ EOF
 is(md5('out.opus'), '66780307a6081523dc9040f3c47b0448', 'the file did not change');
 
 is_deeply(opustags(qw(-i out.opus -a fatal=yes -a FOO -a BAR)), ['', <<'EOF', 256], 'bad tag with --add');
-error: Invalid comment 'FOO'.
+error: Comment does not contain an equal sign: FOO.
 EOF
 is(md5('out.opus'), '66780307a6081523dc9040f3c47b0448', 'the file did not change');
 
@@ -152,7 +152,7 @@ warning: Some tags contain control characters.
 END_ERR
 
 is_deeply(opustags(qw(-i out.opus -s fatal=yes -s FOO -s BAR)), ['', <<'EOF', 256], 'bad tag with --set');
-error: Invalid comment 'FOO'.
+error: Comment does not contain an equal sign: FOO.
 EOF
 is(md5('out.opus'), '66780307a6081523dc9040f3c47b0448', 'the file did not change');