diff --git a/source/games/sw/src/copysect.cpp b/source/games/sw/src/copysect.cpp
index 2b49ece3f..6e92e5e3e 100644
--- a/source/games/sw/src/copysect.cpp
+++ b/source/games/sw/src/copysect.cpp
@@ -246,10 +246,10 @@ void CopySectorMatch(short match)
                 dsectp->extra = ssectp->extra;
                 dsectp->visibility = ssectp->visibility;
 
-                dsectp->portalnum = ssectp->portalnum;
-                dsectp->portalflags = ssectp->portalflags;
-
-                if (ssectp->portalflags & (PORTAL_SECTOR_CEILING|PORTAL_SECTOR_FLOOR)) allPortals[ssectp->portalnum].dx = allPortals[ssectp->portalnum].dy = 0;
+                if (ssectp->floorpicnum == FAF_MIRROR_PIC || ssectp->ceilingpicnum == FAF_MIRROR_PIC)
+                {
+                    CollectPortals(); // unavoidable. Since these portals are not static we have to reinitialize all of them.
+                }
             }
         }
     }
diff --git a/source/games/sw/src/rooms.cpp b/source/games/sw/src/rooms.cpp
index 9f614a576..d41b205b6 100644
--- a/source/games/sw/src/rooms.cpp
+++ b/source/games/sw/src/rooms.cpp
@@ -1029,8 +1029,13 @@ void CollectPortals()
     TArray<PortalGroup> ceilingportals;
     FixedBitArray<MAXSECTORS> floordone, ceilingdone;
 
+    for (int i = 0; i < numsectors; i++)
+    {
+        sector[i].portalflags = sector[i].portalnum = 0;
+    }
     floordone.Zero();
     ceilingdone.Zero();
+    portalClear();
 
     for (int i = 0; i < numsectors; i++)
     {