The current study focused on the production of non-contrastive geminates across different boundary types in English to investigate the hypothesis that word-internal heteromorphemic geminates may differ from those that arise across a word boundary. In this study, word-internal geminates arising from affixation, and described as either assimilated or concatenated, were matched to heteromorphemic geminates arising from sequences of identical consonants that spanned a word boundary and to word-internal singletons. Word-internal geminates were found to be longer than matched singletons in absolute and relative terms. By contrast, heteromorphemic geminates that occurred at word boundaries were only longer than matched singletons in absolute terms. In addition, heteromorphemic geminates in two word phrases were typically "pulled apart" in careful speech; that is, speakers marked the boundaries between free morphemes with pitch changes and pauses. Morpheme boundaries in words with bound affixes were very rarely highlighted in this way. These results are taken to indicate that most word-internal heteromorphemic geminates are represented as a single long consonant in the speech plan rather than as a consonant sequence. Only those geminates that arise in two word phrases exhibit phonetic characteristics that are fully consistent with the representation of two identical consonants crossing a morpheme boundary.