--- a/polygon_clip.hh	2020-05-01 19:47:41.108664761 +0300
+++ b/polygon_clip.hh	2020-06-26 20:47:17.522478319 +0300
@@ -25,10 +25,11 @@
         if((outside < 0 && outsidenext > 0)
         || (outside > 0 && outsidenext < 0))
         {
-            auto factor = outside / (outside - outsidenext);
-
             // Create a new point b between *current and *next like this: current + (next-current) * factor
-            auto b = *current + ((*next - *current) * factor);
+            // The two conditions produces mathematically identical results, but because of floating point,
+            // there may be rounding differences between adjacent walls depending on winding direction.
+            auto b = (outside < outsidenext) ? (*current + (*next - *current) * (outside     / (outside - outsidenext)))
+                                             : (*next    + (*current - *next) * (outsidenext / (outsidenext - outside)));
 
             if(keep) { current = std::next(points.insert(std::next(current), std::move(b))); }
             else     { *current = std::move(b); ++current; }