According to the Interface Hypothesis (IH) (e.g., Tsimpli & Sorace 2006; Sorace 2011), external interfaces are more challenging for L2 learners than internal interfaces. It is not clear, however, if linguistic phenomena associated with external interfaces are necessarily problematic and if internal interfaces are necessarily unproblematic. In order to test these issues, a bidirectional study was conducted with Turkish-speaking learners of English and English-speaking learners of Turkish on the same "quantificational scope" construction, which lies at the interface of semantics, syntax, and pragmatics and thus involves both internal and external interfaces. The task for the former group implicates greater involvement of pragmatics, an external interface, although, for the latter, it involves expunging a construction from the grammar. The results indicate, contra the IH, that whereas the former group has no problems restructuring their grammar, the latter has persistent difficulties.