Index: file.c
===================================================================
--- file.c	(revision 25724)
+++ file.c	(revision 25725)
@@ -638,6 +638,8 @@
 	pcb_layergrp_t *g = pcb_get_grp(&pcb->LayerGroups, loc, typ);
 	if ((g == NULL) || (g->len == 0))
 		return -1;
+	if (g->len > 0)
+		pcb_io_incompat_save(PCB->Data, NULL, "layer", "Multiple silk layers per side not supported by gEDA/PCB", "Merge your silk layers into one layer per group; if there are negative silk layers: layer compositing is not supported by gEDA/PCB");
 	return g->lid[0];
 }