diff --git a/src/ass_dialogue.h b/src/ass_dialogue.h
index d0a8d0f4f..2c3105fe0 100644
--- a/src/ass_dialogue.h
+++ b/src/ass_dialogue.h
@@ -130,6 +130,8 @@ struct AssDialogueBase {
 	/// the different versions of the file.
 	int Id;
 
+	int Row = -1;
+
 	/// Is this a comment line?
 	bool Comment = false;
 	/// Layer number
diff --git a/src/ass_file.cpp b/src/ass_file.cpp
index b90117c59..f1d015a0a 100644
--- a/src/ass_file.cpp
+++ b/src/ass_file.cpp
@@ -164,6 +164,12 @@ AssStyle *AssFile::GetStyle(std::string const& name) {
 }
 
 int AssFile::Commit(wxString const& desc, int type, int amend_id, AssDialogue *single_line) {
+	if (type == COMMIT_NEW || (type & COMMIT_DIAG_ADDREM)) {
+		int i = 0;
+		for (auto& event : Events)
+			event.Row = i++;
+	}
+
 	PushState({desc, &amend_id, single_line});
 
 	std::set<const AssDialogue*> changed_lines;
diff --git a/src/base_grid.cpp b/src/base_grid.cpp
index c78ac8239..77040ed87 100644
--- a/src/base_grid.cpp
+++ b/src/base_grid.cpp
@@ -228,12 +228,9 @@ void BaseGrid::UpdateStyle() {
 
 void BaseGrid::UpdateMaps() {
 	index_line_map.clear();
-	line_index_map.clear();
 
-	for (auto& curdiag : context->ass->Events) {
-		line_index_map[&curdiag] = (int)index_line_map.size();
+	for (auto& curdiag : context->ass->Events)
 		index_line_map.push_back(&curdiag);
-	}
 
 	SetColumnWidths();
 	AdjustScrollbar();
@@ -242,7 +239,7 @@ void BaseGrid::UpdateMaps() {
 
 void BaseGrid::OnActiveLineChanged(AssDialogue *new_active) {
 	if (new_active) {
-		int row = GetDialogueIndex(new_active);
+		int row = new_active->Row;
 		MakeRowVisible(row);
 		extendRow = row;
 		Refresh(false);
@@ -792,11 +789,6 @@ AssDialogue *BaseGrid::GetDialogue(int n) const {
 	return index_line_map[n];
 }
 
-int BaseGrid::GetDialogueIndex(AssDialogue *diag) const {
-	auto it = line_index_map.find(diag);
-	return it != line_index_map.end() ? it->second : -1;
-}
-
 bool BaseGrid::IsDisplayed(const AssDialogue *line) const {
 	if (!context->videoController->IsLoaded()) return false;
 	int frame = context->videoController->GetFrameN();
@@ -856,8 +848,9 @@ void BaseGrid::OnKeyDown(wxKeyEvent &event) {
 		return;
 	}
 
+	auto active_line = context->selectionController->GetActiveLine();
 	int old_extend = extendRow;
-	int next = mid(0, GetDialogueIndex(context->selectionController->GetActiveLine()) + dir * step, GetRows() - 1);
+	int next = mid(0, (active_line ? active_line->Row : 0) + dir * step, GetRows() - 1);
 	context->selectionController->SetActiveLine(GetDialogue(next));
 
 	// Move selection
diff --git a/src/base_grid.h b/src/base_grid.h
index baf3a5b9f..38066de07 100644
--- a/src/base_grid.h
+++ b/src/base_grid.h
@@ -34,7 +34,6 @@
 
 #include <libaegisub/signal.h>
 
-#include <map>
 #include <memory>
 #include <vector>
 #include <wx/window.h>
@@ -59,7 +58,6 @@ class BaseGrid final : public wxWindow {
 	int extendRow = -1;
 
 	std::vector<AssDialogue*> index_line_map;  ///< Row number -> dialogue line
-	std::map<AssDialogue*,int> line_index_map; ///< Dialogue line -> row number
 
 	/// Connection for video seek event. Stored explicitly so that it can be
 	/// blocked if the relevant option is disabled
@@ -120,11 +118,6 @@ class BaseGrid final : public wxWindow {
 	/// @return Subtitle dialogue line for index, or 0 if invalid index
 	AssDialogue *GetDialogue(int n) const;
 
-	/// @brief Get index by dialogue line
-	/// @param diag Dialogue line to look up
-	/// @return Subtitle index for object, or -1 if unknown subtitle
-	int GetDialogueIndex(AssDialogue *diag) const;
-
 public:
 	BaseGrid(wxWindow* parent, agi::Context *context);
 	~BaseGrid();