Hi all, I found that mkgmap can display an exception with a confusing description : Time started: Wed Feb 10 14:27:05 CET 2016 GRAVE (SeaGenerator): D:\tmp\idf-generic\14070303.osm.pbf: Cannot read index file index.txt.gz java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.<init>(ZipFile.java:215) at java.util.zip.ZipFile.<init>(ZipFile.java:145) at java.util.zip.ZipFile.<init>(ZipFile.java:159) at uk.me.parabola.mkgmap.reader.osm.SeaGenerator.init(SeaGenerator.java:161) at uk.me.parabola.mkgmap.reader.osm.OsmMapDataSource.pluginChain(OsmMapDataSource.java:209) at uk.me.parabola.mkgmap.reader.osm.OsmMapDataSource.setupHandler(OsmMapDataSource.java:180) at uk.me.parabola.mkgmap.reader.osm.bin.OsmBinMapDataSource.load(OsmBinMapDataSource.java:49) at uk.me.parabola.mkgmap.reader.osm.OsmMapDataSource.load(OsmMapDataSource.java:130) at uk.me.parabola.mkgmap.main.MapMaker.loadFromFile(MapMaker.java:154) at uk.me.parabola.mkgmap.main.MapMaker.makeMap(MapMaker.java:52) at uk.me.parabola.mkgmap.main.Main$1.call(Main.java:255) at uk.me.parabola.mkgmap.main.Main$1.call(Main.java:251) at java.util.concurrent.FutureTask.run(FutureTask.java:262) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) At first, I understood that the pbf file is corrupted (this exception is thrown for each .pbf file). Actually, the pbf files are OK : the error is the sea.zip file that is corrupted. I improved the error reporting in the attached patch. I'd like to have mkgmap fail when this happens but I don't know how to do that. Lambertus, I think you're the person providing the sea and bounds files at http://osm2.pleiades.uni-wuppertal.de/ , can you provide a checksum file for these files in order to detect bad downloads ? Thanks, Paco