diff --git a/include/defs.h b/include/defs.h
index 470bf1d..57f6d2f 100644
--- a/include/defs.h
+++ b/include/defs.h
@@ -382,6 +382,10 @@ void            vga_putc(int, uint32);
 void            vga_clear(uint32);
 void            vga_screen_reset(void);
 void            vga_set_bg(uint32);
+// The mode actually in use. The resolution is a boot-time choice now, so no
+// caller may hardcode it.
+uint32          vga_get_width(void);
+uint32          vga_get_height(void);
 // Crash-screen primitives: the panic handler lays itself out rather than
 // printing. See kernel/core/panic.c.
 int             vga_ready(void);
diff --git a/kernel/dev/mouse.c b/kernel/dev/mouse.c
index 3f3a25f..029c6f7 100644
--- a/kernel/dev/mouse.c
+++ b/kernel/dev/mouse.c
@@ -66,10 +66,20 @@ mouse_move_locked(int dx, int dy)
   mouse_state.x += dx;
   mouse_state.y += dy;
 
+  // Clamp to the screen that actually exists. These were the literals 800 and
+  // 600, which was correct while that was the only mode the loader could set.
+  // It is a boot-time choice now (press R), and at 1280x800 the pointer simply
+  // stopped two thirds of the way across -- which reads as the cursor drifting
+  // away from the host's, rather than as a clamp.
+  int maxx = (int)vga_get_width();
+  int maxy = (int)vga_get_height();
+  if(maxx <= 0) maxx = 800;
+  if(maxy <= 0) maxy = 600;
+
   if(mouse_state.x < 0) mouse_state.x = 0;
   if(mouse_state.y < 0) mouse_state.y = 0;
-  if(mouse_state.x >= 800) mouse_state.x = 799;
-  if(mouse_state.y >= 600) mouse_state.y = 599;
+  if(mouse_state.x >= maxx) mouse_state.x = maxx - 1;
+  if(mouse_state.y >= maxy) mouse_state.y = maxy - 1;
 }
 
 // The same pointer, moved by something that is not the PS/2 port. USB HID
diff --git a/kernel/dev/vga.c b/kernel/dev/vga.c
index abe51ad..63af1ca 100644
--- a/kernel/dev/vga.c
+++ b/kernel/dev/vga.c
@@ -73,6 +73,20 @@ vga_init(uint64 phys_addr) {
   // when userspace starts and the display changes owner.
 }
 
+// The mode that was actually set. Exported because the resolution is chosen at
+// boot now (press R -- see boot/bios/stage2.S), so nothing above may assume it.
+uint32
+vga_get_width(void)
+{
+  return vga_width;
+}
+
+uint32
+vga_get_height(void)
+{
+  return vga_height;
+}
+
 void
 vga_draw_pixel(int x, int y, uint32 color)
 {