Index: trunk/src/thermal.c
===================================================================
--- trunk/src/thermal.c	(revision 27906)
+++ trunk/src/thermal.c	(revision 27907)
@@ -709,14 +709,20 @@
 	unsigned char thr;
 	pcb_pstk_shape_t *shp, tmpshp;
 	pcb_polyarea_t *pres = NULL;
-	pcb_layer_t *layer = pcb_get_layer(pcb->Data, lid);
+	pcb_layer_t *layer;
 	pcb_coord_t clearance = ps->Clearance;
 
+	/* thermal needs a stackup - only a PCB has a stackup, buffers don't */
+	if (pcb == NULL)
+		return NULL;
+
 	/* if we have no clearance, there's no reason to do anything;
 	   ps->Clearance == 0 doesn't mean no clearance because of the per shape clearances */
 	if (!PCB_FLAG_TEST(PCB_FLAG_CLEARLINE, ps))
 		return NULL;
 
+	layer = pcb_get_layer(pcb->Data, lid);
+
 	/* retrieve shape; assume 0 (no shape) for layers not named */
 	if (lid < ps->thermals.used)
 		thr = ps->thermals.shape[lid];