diff --git a/aegisub/src/base_grid.cpp b/aegisub/src/base_grid.cpp
index 6d6453e72..b9d4d2a14 100644
--- a/aegisub/src/base_grid.cpp
+++ b/aegisub/src/base_grid.cpp
@@ -38,6 +38,7 @@
 
 #ifndef AGI_PRE
 #include <algorithm>
+#include <cmath>
 #include <iterator>
 
 #include <wx/dcclient.h>
@@ -174,6 +175,8 @@ void BaseGrid::UpdateMaps(bool preserve_selected_rows) {
 			bind1st(std::mem_fun(&BaseGrid::GetDialogueIndex), this));
 	}
 
+	size_t old_diag_count = index_line_map.size();
+
 	index_line_map.clear();
 	line_index_map.clear();
 
@@ -244,6 +247,9 @@ void BaseGrid::UpdateMaps(bool preserve_selected_rows) {
 
 	EndBatch();
 
+	if ((int)log10((double)old_diag_count) != (int)log10((double)index_line_map.size()))
+		SetColumnWidths();
+
 	Refresh(false);
 }