diff --git a/source/sw/src/rooms.cpp b/source/sw/src/rooms.cpp
index 420d3a565..90e07d57e 100644
--- a/source/sw/src/rooms.cpp
+++ b/source/sw/src/rooms.cpp
@@ -830,9 +830,10 @@ GetUpperLowerSector(short match, int x, int y, short *upper, short *lower)
                 if (!found)
                     continue;
 
-                sectorlist[sln] = i;
                 if (sln < (int)SIZ(GlobStackSect))
                     GlobStackSect[sln] = i;
+                if (sln < (int)SIZ(sectorlist))
+                    sectorlist[sln] = i;
                 sln++;
             }
         }