diff --git a/src/GPU3D_Soft.h b/src/GPU3D_Soft.h
index a4342431..4783dff3 100644
--- a/src/GPU3D_Soft.h
+++ b/src/GPU3D_Soft.h
@@ -145,7 +145,7 @@ private:
 
         constexpr s32 Interpolate(s32 y0, s32 y1) const
         {
-            if (x == 0 || y0 == y1) return y0;
+            if (x == 0 || xdiff == 0 ||  y0 == y1) return y0;
 
             if (!linear)
             {
@@ -167,7 +167,7 @@ private:
 
         constexpr s32 InterpolateZ(s32 z0, s32 z1)
         {
-            if (x == 0 || z0 == z1) return z0;
+            if (x == 0 || xdiff == 0 || z0 == z1) return z0;
 
             if (wbuffer)
             {