Because the appearance of the passive construction varies cross linguistically, differences exist in the interlanguage (IL) passives attempted by learners of English. One such difference is the widely studied IL pseudo passive, as in "*new cars must keep inside" produced by Chinese speakers. The belief that this is a reflection of L1 language typology has led to the study of passive constructions produced by Thai speakers. It was, however, discovered that only a small number of IL pseudo passives have emerged in the data. Instead, most problematic passives concerned malformed past participles. These unexpected results are likely due to the language proficiency of the Thai subjects and the differences between Thai and Chinese. (Contains 5 tables and 8 footnotes.)