diff --git a/backend/rts8891.c b/backend/rts8891.c
index dfb5b11ef..fcb2669e6 100644
--- a/backend/rts8891.c
+++ b/backend/rts8891.c
@@ -5887,7 +5887,7 @@ shading_calibration (struct Rts8891_Device *dev, SANE_Bool color, int mode,
 	  dev->regs[0x88] = 0x10;
 	  dev->regs[0x89] = 0xb2;
 	  dev->regs[0x8a] = 0x00;
-	  dev->regs[0x8d] = 0x77;
+	  dev->regs[0x8d] = 0x3b; /* 0x77 */
 	  dev->regs[0x8e] = 0x60;
 	  dev->regs[0xc0] = 0xf8;
 	  dev->regs[0xc1] = 0x7f;
@@ -7306,7 +7306,7 @@ write_scan_registers (struct Rts8891_Session *session)
 	  dev->regs[0x35] = 0x1b;
 	  dev->regs[0x36] = 0x29;
 	  dev->regs[0x3a] = 0x1b;
-	  dev->regs[0x40] = 0x24;
+	  dev->regs[0x40] = 0x2c; /* 0x24 */
 	  dev->regs[0x50] = 0x00; /* 0x18 */
 	  dev->regs[0x64] = 0x01; /* 0x02 */
 	  dev->regs[0x65] = 0x20; /* 0x10 */