Methods for making a synthetic nucleic acid which comprise: (a) identifying a conflicting nucleotide sequence in a target sequence; (b) inserting a masking sequence into the conflicting sequence to produce a disrupted target sequence, wherein: (i) the masking sequence comprises recognition sites for one or more Type IIS restriction endonucleases; and (ii) digestion of said disrupted target sequence by said one or more Type IIS restriction endonucleases followed by re-ligation reconstitutes the target sequence; (c) synthesizing a polynucleotide comprising the disrupted target sequence using polymerase chain assembly; and (d) removing the masking sequence from said polynucleotide by digesting said polynucleotide with said one or more Type IIS restriction endonucleases followed by re-ligation of the digestion product, thereby producing a polynucleotide comprising said target sequence.