[KyleGoetz]

Yeah, MMM, you're right. I haven't had to write the word for a while, and it's so darn hard to end a word orally with っど. I think in my mind I was thinking about how ベッド is the exception to the rule that Japanese words cannot generally end in っど. I might be willing to extend my linguistic description there to: "Japanese words cannot (or very rarely can) end in an glottal stop followed by a voiced consonant and a vowel."

How many words can we think of that end in っだ／っぢ／っづ／っで／っど／っが／っぎ／っぐ／っ げ／っご／っば／っび／っぶ／っべ／っぼ etc.?

I can only think of ベッド, but there has to be a few (albeit a very few) others.

Edit: I guess, technically, only p,t,k, and s can be doubled in native Japanese words anyway (in general?).