diff --git a/src/p_floor.cpp b/src/p_floor.cpp
index 68602ab0a..5c21f771d 100644
--- a/src/p_floor.cpp
+++ b/src/p_floor.cpp
@@ -663,9 +663,8 @@ bool EV_BuildStairs (int tag, DFloor::EStair type, line_t *line,
 						sec = tsec;
 						continue;
 					}
-					
+					newsecnum = tsec->Index();
 				}
-				newsecnum = (int)(tsec - sectors);
 			}
 			else
 			{