diff --git a/src/fenigma/grid_widget.py b/src/fenigma/grid_widget.py
index fafdf99..3ae1774 100644
--- a/src/fenigma/grid_widget.py
+++ b/src/fenigma/grid_widget.py
@@ -117,6 +117,12 @@ class GridCanvas(Gtk.DrawingArea):
         self.on_right_click = None  # callback(Coord, x, y), fired on right-click (unless placing)
         self.hide_dead_from_map = False  # off by default; toggled from the firing panel toolbar
 
+        # Which large cell the cursor is currently over, (col, row) both
+        # floored, or None off the map/off the widget entirely. Redrawn
+        # only when this actually changes cell (not on every pixel of
+        # motion within the same one), see _draw_hover_subgrid().
+        self._hover_cell: tuple[int, int] | None = None
+
         # Placement mode: while armed, the next left-click calls
         # placement_callback(Coord) instead of doing the normal
         # select/hit-test, and (if placement_preview_radius_km is set) a
@@ -423,6 +429,12 @@ class GridCanvas(Gtk.DrawingArea):
         if self.on_cursor_move is not None:
             self.on_cursor_move(cursor_km)
 
+        col, row = cursor_km
+        new_cell = (int(col), int(row)) if (0 <= col < COLS and 0 <= row < ROWS) else None
+        if new_cell != self._hover_cell:
+            self._hover_cell = new_cell
+            self.queue_draw()
+
         if self.placement_callback is not None:
             self._placement_cursor_km = cursor_km
             self.queue_draw()
@@ -440,6 +452,9 @@ class GridCanvas(Gtk.DrawingArea):
         self._last_pointer_px = None
         if self.on_cursor_move is not None:
             self.on_cursor_move(None)
+        if self._hover_cell is not None:
+            self._hover_cell = None
+            self.queue_draw()
         if self.placement_callback is not None:
             self._placement_cursor_km = None
             self.queue_draw()
@@ -552,6 +567,7 @@ class GridCanvas(Gtk.DrawingArea):
         cr.rectangle(MARGIN_LEFT + view.pad_x, MARGIN_TOP + view.pad_y, view.grid_w, view.grid_h)
         cr.clip()
 
+        self._draw_hover_subgrid(cr, view)
         self._draw_geo_overlays(cr, view)
         self._draw_firing_arrows(cr, view)
         self._draw_blast_radius(cr, view)
@@ -600,6 +616,29 @@ class GridCanvas(Gtk.DrawingArea):
 
         cr.restore()
 
+    def _draw_hover_subgrid(self, cr, view) -> None:
+        """The fine 10x10 x:y subdivision lines for whichever large
+        cell the cursor is currently over, for precise sub-cell
+        targeting, most useful once zoomed in enough that a single
+        large cell actually has room to show them meaningfully."""
+        if self._hover_cell is None:
+            return
+        cell_col, cell_row = self._hover_cell
+        r, g, b, a = GRID_LINE
+        cr.set_source_rgba(r, g, b, a * 0.6)  # fainter than the plain grid lines, not louder
+        cr.set_line_width(1)
+        x0, y0 = self._km_to_px(view, (cell_col, cell_row))
+        x1, y1 = self._km_to_px(view, (cell_col + 1, cell_row + 1))
+        for i in range(1, 10):
+            x, _ = self._km_to_px(view, (cell_col + i / 10, cell_row))
+            cr.move_to(x, y0)
+            cr.line_to(x, y1)
+        for i in range(1, 10):
+            _, y = self._km_to_px(view, (cell_col, cell_row + i / 10))
+            cr.move_to(x0, y)
+            cr.line_to(x1, y)
+        cr.stroke()
+
     def _draw_marker(self, cr, view, point_km, color, label,
                       canvas_width, canvas_height, *, hollow=False, dim=False,
                       selected=False, coord=None, extra_line=None, icon_surface=None) -> None: