Index: data.c
===================================================================
--- data.c	(revision 16971)
+++ data.c	(revision 16972)
@@ -581,7 +581,14 @@
 				} PCB_ENDALL_LOOP;
 				ctx->inited = 1;
 			}
-			pcb_gui->progress(ctx->at, ctx->total, "Clipping polygons...");
+			if (pcb_gui->progress(ctx->at, ctx->total, "Clipping polygons...") != 0) {
+				if (pcb_gui->confirm_dialog("The only way to cancel poly clipping is to quit pcb-rnd.\nAre you sure you want to quit?", "yes, quit", "no, continue", NULL) != 0) {
+					/* Have to recreate the dialog next time, that's the only way to get it out from the cancel state */
+					pcb_gui->progress(0, 0, NULL);
+				}
+				else
+					exit(1);
+			}
 		}
 	}
 }