Part A of Appendix 9 - Orthography of the International Code of Nomenclature of Prokaryotes regulates the formation of compound generic names and specific epithets derived by combining two or more words or word elements of Latin and/or Greek origin, using the word stems and connecting vowels (-o- or -i-) following word elements derived from Greek and Latin, respectively. The rules given and the exceptions listed are suitable for substantives (nouns) and adjectives used as word elements, but not for prepositions and prefixes. Therefore, we propose a non-retroactive modification of Appendix 9 so that the guidelines given in Part A apply only to compound names that include a noun or an adjective in a non-final position. We also propose guidelines for the proper use of Greek and Latin prepositions, prefixes and adverbs in compound names in which the following word element starts with a vowel.