This theoretical position article presents the current state of the research on college-aged Spanish heritage language learners' (HL) spelling as well as the limitations of a descriptive approach to spelling research. The article also highlights the need to analyze and understand HLs' errors based on the underlying cognitive-linguistic processes behind the assignation of graphemes to phonemes. In this article, I analyze Spanish misspellings in college-age HLs within a cognitive-linguistic framework. Spelling is not merely a system of phoneme-grapheme correspondences prescriptively established, but it also requires acquiring and developing awareness of the language's phonological and morphological codes. This article reviews those two cognitive domains and examines different types of spelling errors made by HLs under this perspective, by showing the role of each of these cognitive skills in the erroneous assignment of graphemes to phonemes. Furthermore, the article suggests lines of experimental research targeting these cognitive-linguistic domains.