diff --git a/src/rs.cpp b/src/rs.cpp
index aedfb19b32..f15475fe9d 100644
--- a/src/rs.cpp
+++ b/src/rs.cpp
@@ -3720,7 +3720,7 @@ void next_pixel_in_line(float curr[2], const float start[2], const float end[2])
     else
     {
         curr[1] = end[1] > curr[1] ? curr[1] + 1 : curr[1] - 1;
-        curr[0] = end[0] - ((end[1] + curr[1]) / line_slope);
+        curr[0] = end[0] - ((end[1] - curr[1]) / line_slope);
     }
 }