Code-blending is the simultaneous expression of utterances using both a sign language and a spoken language. We expect that like code-switching, code-blending is linguistically constrained and thus we investigate two hypothesized constraints using an acceptability judgment task. Participants rated the acceptability of code-blended utterances designed to be consistent or inconsistent with these hypothesized constraints. We find strong support for the proposed constraint that each modality of code-blended utterances contributes content to a single proposition. We also find support for the proposed constraint that – at least for American Sign Language (ASL) and English – code-blended utterances make use of a single derivation which is realized using surface forms in the two languages, rather than two simultaneous derivations, one for each language. While this study was limited to ASL/English code-blending and further investigation is needed, we hope that this novel study will encourage future research comparing linguistic constraints on code-blending and code-switching.