diff --git a/src/r_data/r_interpolate.cpp b/src/r_data/r_interpolate.cpp
index d153b3a781..82e27abb48 100644
--- a/src/r_data/r_interpolate.cpp
+++ b/src/r_data/r_interpolate.cpp
@@ -261,9 +261,12 @@ void FInterpolator::DoInterpolations(fixed_t smoothratio)
 
 	didInterp = true;
 
-	for (DInterpolation *probe = Head; probe != NULL; probe = probe->Next)
+	DInterpolation *probe = Head;
+	while (probe != NULL)
 	{
+		DInterpolation *next = probe->Next;
 		probe->Interpolate(smoothratio);
+		probe = next;
 	}
 }
 
@@ -444,6 +447,8 @@ void DSectorPlaneInterpolation::UpdateInterpolation()
 		oldheight = sector->ceilingplane.d;
 		oldtexz = sector->GetPlaneTexZ(sector_t::ceiling);
 	}
+	if (oldtexz <-128*FRACUNIT)
+		__asm nop
 }
 
 //==========================================================================