Academia and the public media have emphasized the link between STEM majors and innovation, as well as the need for STEM graduates in the U.S. economy. Given the proclivity of international students to hold STEM degrees, immigration policy may be used to attract and retain high-skilled STEM workers in the United States. We examine if a 2008 policy extending the Optional Practical Training (OPT) period for STEM graduates affected international students' propensities to major in a STEM field. Using data from the National Survey of College Graduates, we find that, relative to foreign-born U.S. college graduates who arrived on other visas allowing them to work, foreign-born students who first came to the United States on student visas became 18 percent more likely to major in STEM following the OPT policy change. We also find that the OPT policy change increased the likelihood of adding a STEM major among students who had listed a non-STEM major as their first major, as well as the propensity to pursue a master's degree in a STEM field among students whose bachelor's degree was in a non-STEM field.