diff --git a/src/ass_karaoke.cpp b/src/ass_karaoke.cpp
index cc55f6143..ee47115e7 100644
--- a/src/ass_karaoke.cpp
+++ b/src/ass_karaoke.cpp
@@ -39,11 +39,11 @@ std::string AssKaraoke::Syllable::GetText(bool k_tag) const {
 	return ret;
 }
 
-AssKaraoke::AssKaraoke(AssDialogue *line, bool auto_split, bool normalize) {
+AssKaraoke::AssKaraoke(const AssDialogue *line, bool auto_split, bool normalize) {
 	if (line) SetLine(line, auto_split, normalize);
 }
 
-void AssKaraoke::SetLine(AssDialogue *line, bool auto_split, bool normalize) {
+void AssKaraoke::SetLine(const AssDialogue *line, bool auto_split, bool normalize) {
 	syls.clear();
 	Syllable syl;
 	syl.start_time = line->Start;
@@ -87,7 +87,7 @@ void AssKaraoke::SetLine(AssDialogue *line, bool auto_split, bool normalize) {
 	AnnounceSyllablesChanged();
 }
 
-void AssKaraoke::ParseSyllables(AssDialogue *line, Syllable &syl) {
+void AssKaraoke::ParseSyllables(const AssDialogue *line, Syllable &syl) {
 	for (auto& block : line->ParseTags()) {
 		std::string text = block->GetText();
 
diff --git a/src/ass_karaoke.h b/src/ass_karaoke.h
index fd929f867..9802957fa 100644
--- a/src/ass_karaoke.h
+++ b/src/ass_karaoke.h
@@ -46,17 +46,17 @@ private:
 	bool no_announce = false;
 
 	agi::signal::Signal<> AnnounceSyllablesChanged;
-	void ParseSyllables(AssDialogue *line, Syllable &syl);
+	void ParseSyllables(const AssDialogue *line, Syllable &syl);
 
 public:
 	/// Constructor
 	/// @param line Initial line
 	/// @param auto_split Should the line automatically be split on spaces if there are no k tags?
 	/// @param normalize Should the total duration of the syllables be forced to equal the line duration?
-	AssKaraoke(AssDialogue *line = nullptr, bool auto_split = false, bool normalize = true);
+	AssKaraoke(const AssDialogue *line = nullptr, bool auto_split = false, bool normalize = true);
 
 	/// Parse a dialogue line
-	void SetLine(AssDialogue *line, bool auto_split = false, bool normalize = true);
+	void SetLine(const AssDialogue *line, bool auto_split = false, bool normalize = true);
 
 	/// Add a split before character pos in syllable syl_idx
 	void AddSplit(size_t syl_idx, size_t pos);