diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 905f27326..6df94d23d 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,5 @@
 October 24, 2009  (Changes by Graf Zahl)
+- fixed: sector_t::GetHeightSec checked the wrong MoreFlags.
 - made max. view pitch a property of the renderer so that it's overridable without
   changing game code.
 - made SpawningMapThing an argument of AActor::StaticSpawn instead of a global
diff --git a/src/r_defs.h b/src/r_defs.h
index 88f4e98a8..623e475c4 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -588,7 +588,7 @@ struct sector_t
 
 	sector_t *GetHeightSec() const 
 	{
-		return (MoreFlags & SECF_IGNOREHEIGHTSEC)? NULL : heightsec;
+		return (heightsec && !(heightsec->MoreFlags & SECF_IGNOREHEIGHTSEC))? heightsec : NULL;
 	}
 
 	void ChangeLightLevel(int newval)