In emulation of a target system on a host system one or more blocks of target system code may be translated with the host system to produce one or more corresponding blocks of translated code. Translating the target system code may include linking two or more blocks of translated code together to form a chain such that a look-up in a first translated block in the chain will directly branch to a second translated block. The target system code may be analyzed for the presence of one or more native target system instructions indicating modification of the target system code during execution. If such native target system instructions are present some or all of the blocks of translated code may be marked potentially invalid. The one or more blocks marked as potentially invalid may be re-translated and one or more instructions in the blocks of translated code may be overridden without undoing the chain.