Methods of code conversion are provided. Aspects include obtaining a first code point from a source data string in a first character encoding, wherein the source data string is to be converted to a target data string in a second character encoding. A target code point corresponding to the first code point is looked up in a map table, wherein the target code point is in the second character encoding. It is determined whether the first code point is a first combining character in response to receiving a lookup failure generated from the looking up operation. A combination unit having the first combining character and a base character next to the first combining character in the source data string is identified in response to determining that the first code point is the first combining character. The combination unit is converted to a substitute character in the target data string.