diff --git a/grid.c b/grid.c
index 5a0b5c7e..4a3995a0 100644
--- a/grid.c
+++ b/grid.c
@@ -15,6 +15,34 @@
 
 #define TIME_REFLOW 0
 
+/*
+ * “sb” (scrollback relative) coordinates
+ *
+ * The scrollback relative row number 0 is the *first*, and *oldest*
+ * row in the scrollback history (and thus the *first* row to be
+ * scrolled out). Thus, a higher number means further *down* in the
+ * scrollback, with the *highest* number being at the bottom of the
+ * screen, where new input appears.
+ */
+int
+grid_row_abs_to_sb(const struct grid *grid, int screen_rows, int abs_row)
+{
+    const int scrollback_start = grid->offset + screen_rows;
+    int rebased_row = abs_row - scrollback_start + grid->num_rows;
+
+    rebased_row &= grid->num_rows - 1;
+    return rebased_row;
+}
+
+int grid_row_sb_to_abs(const struct grid *grid, int screen_rows, int sb_rel_row)
+{
+    const int scrollback_start = grid->offset + screen_rows;
+    int abs_row = sb_rel_row + scrollback_start;
+
+    abs_row &= grid->num_rows - 1;
+    return abs_row;
+}
+
 static void
 ensure_row_has_extra_data(struct row *row)
 {
diff --git a/grid.h b/grid.h
index 7819db4d..22bd76bb 100644
--- a/grid.h
+++ b/grid.h
@@ -21,6 +21,10 @@ void grid_resize_and_reflow(
     size_t tracking_points_count,
     struct coord *const _tracking_points[static tracking_points_count]);
 
+/* Convert row numbers between scrollback-relative and absolute coordinates */
+int grid_row_abs_to_sb(const struct grid *grid, int screen_rows, int abs_row);
+int grid_row_sb_to_abs(const struct grid *grid, int screen_rows, int sb_rel_row);
+
 static inline int
 grid_row_absolute(const struct grid *grid, int row_no)
 {
@@ -33,6 +37,7 @@ grid_row_absolute_in_view(const struct grid *grid, int row_no)
     return (grid->view + row_no) & (grid->num_rows - 1);
 }
 
+
 static inline struct row *
 _grid_row_maybe_alloc(struct grid *grid, int row_no, bool alloc_if_null)
 {