Modern linguistic theory posits the existence of universal constraints. But whether these constraints concern language structure, generally, or speech, specifically, is unknown. To address this question, here we ask whether the constraints identified in spoken languages transfer to sign languages. ANCHORING (McCarthy & Prince, 1993) is a putatively universal constraint on reduplication. ANCHORING requires that the final element of a suffixed reduplicant match the final element of the base (e.g., pana ‘chase’––>panana, ‘run’ not panapa). Here, we examine whether ANCHORING is likewise operative in a signed language. In our experiments, native ASL signers rated novel reduplicated forms: either ones consistent or inconsistent with ANCHORING (i.e., ABB vs. ABA, where A and B are syllables). Results showed that signers reliably favored ABB forms over ABA. These findings show for the first time that ANCHORING constrains a sign language. This conclusion is consistent with the existence of amodal linguistic principles.