diff --git a/src/gallium/drivers/softpipe/sp_setup.c b/src/gallium/drivers/softpipe/sp_setup.c
index 478d8efd1b2..4cd11ddc69d 100644
--- a/src/gallium/drivers/softpipe/sp_setup.c
+++ b/src/gallium/drivers/softpipe/sp_setup.c
@@ -805,7 +805,6 @@ line_persp_coeff(const struct setup_context *setup,
                  struct tgsi_interp_coef *coef,
                  uint vertSlot, uint i)
 {
-   /* XXX double-check/verify this arithmetic */
    const float a0 = setup->vmin[vertSlot][i] * setup->vmin[0][3];
    const float a1 = setup->vmax[vertSlot][i] * setup->vmax[0][3];
    const float da = a1 - a0;
@@ -813,7 +812,7 @@ line_persp_coeff(const struct setup_context *setup,
    const float dady = da * setup->emaj.dy * setup->oneoverarea;
    coef->dadx[i] = dadx;
    coef->dady[i] = dady;
-   coef->a0[i] = (setup->vmin[vertSlot][i] -
+   coef->a0[i] = (a0 -
                   (dadx * (setup->vmin[0][0] - setup->pixel_offset) +
                    dady * (setup->vmin[0][1] - setup->pixel_offset)));
 }