Even though I passed "UTF-8" as encoding type PHP (Version 4.3.3) did *not* treat the input file as UTF-8. The input file was missing the BOM header bytes (which may indeed be omitted, according to RFC3629...but things are a bit unclear there. The RFC seems to make mere recommendations concering the BOM header). If you want to sure that PHP treats an UTF-8 encoded file correctly, make sure that it begins with the corresponding 3 byte BOM header (0xEF 0xBB 0xBF)