diff --git a/src/gallium/auxiliary/vl/vl_zscan.c b/src/gallium/auxiliary/vl/vl_zscan.c
index ef05af4..24d6452 100644
--- a/src/gallium/auxiliary/vl/vl_zscan.c
+++ b/src/gallium/auxiliary/vl/vl_zscan.c
@@ -152,7 +152,7 @@
    for (i = 0; i < zscan->num_channels; ++i) {
       ureg_ADD(shader, ureg_writemask(tmp, TGSI_WRITEMASK_X), ureg_scalar(ureg_src(tmp), TGSI_SWIZZLE_Y),
                ureg_imm1f(shader, 1.0f / (zscan->blocks_per_line * VL_BLOCK_WIDTH)
-                * (i - (signed)zscan->num_channels / 2)));
+                * ((signed)i - (signed)zscan->num_channels / 2)));
 
       ureg_MAD(shader, ureg_writemask(o_vtex[i], TGSI_WRITEMASK_X), vrect,
                ureg_imm1f(shader, 1.0f / zscan->blocks_per_line), ureg_src(tmp));