diff --git a/src/r_defs.h b/src/r_defs.h
index 18eba3b7b..6ad406eca 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -1289,7 +1289,8 @@ inline void AActor::ClearInterpolation()
 	PrevY = Y();
 	PrevZ = Z();
 	PrevAngle = angle;
-	PrevPortalGroup = Sector->PortalGroup;
+	if (Sector) PrevPortalGroup = Sector->PortalGroup;
+	else PrevPortalGroup = 0;
 }