diff --git a/source/sw/src/sector.cpp b/source/sw/src/sector.cpp
index 0f0e5a5a8..c8535df7f 100644
--- a/source/sw/src/sector.cpp
+++ b/source/sw/src/sector.cpp
@@ -197,8 +197,9 @@ WallSetup(void)
                  wall_num = wall[wall_num].point2)
             {
                 SET(wall[wall_num].extra, WALLFX_LOOP_DONT_SPIN);
-                if (wall[wall_num].nextwall >= 0) 
-					SET(wall[wall[wall_num].nextwall].extra, WALLFX_LOOP_DONT_SPIN);
+                auto const nextwall = wall[wall_num].nextwall;
+                if ((unsigned)nextwall < MAXSECTORS)
+                    SET(wall[nextwall].extra, WALLFX_LOOP_DONT_SPIN);
             }
 
             break;