You are right, Casper, but French people don't use the feminine "ma" before words that start with a vowel. In this case, they use the masculine one: "mon amie" and not *"ma amie", to prevent the colliding of two identical vowels. This is called "euphonics".
The same thing occurs in Spanish with the singular definite article: they say "el agua", "el águila", even being both nouns feminine.
But in Spanish it doesn't apply to every feminine noun beginning by an "a", it only applies if the "a" is stressed.
la aMIga
el HAda
una aLONdra
un ANcla