When I enable assertions (-ea) in my java command, mkgmap-r3300 is not able to produce one tile and gives an java.lang.AssertionError. I found out that the problem was this turn restriction relation, with type=restriction:motorcar restriction=only_straight_on http://www.openstreetmap.org/relation/3490966 In my relation style file I have the following line, to ignore those restrictions in my bike map: type=restriction:motorcar {delete type} I dont know if it's a bug in mkgmap or in my styles but it will produce no errors without this line, but then the restriction are applied and that's not what is intended. If I change the line into type=restriction:motorcar {delete 'type=restriction:motorcar'} then I get no assertion error. Now maybe this relation is a bad case because mkgmap seems to ignore it at all (via ways instead of via-points?) so I have adapted the relation a bit in JOSM to make it work with one 'from' way, one via-point and one 'to' way. http://mijndev.openstreetmap.nl/~ligfietser/test/map.osm I use in my relation file this line type=restriction:motorcar {delete 'type=restriction:motorcar'} Result is that in motorcar mode, the turn restriction is still active. So there is still something missing in the mkgmap code, also {delete restriction} didnt help here either, looks like that those lines are completely ignored in the relation file here?