git-am: can't apply to an empty repository

When trying to build a repository from mbox format patches I have the
following problem:

Creating a hypothetical mbox patch:

$ echo "From: imre deak [off-list ref]" > 1.patch
$ touch a
$ git diff --no-index /dev/null a >> 1.patch
$ cat 1.patch
From: imre deak <redacted>

diff --git a/a b/a
new file mode 100644
index 0000000..e69de29

Apply it to a newly created repository:

$ git init
Initialized empty Git repository in /home/imde/conv/git/.git/
$ git am 1.patch
fatal: HEAD: not a valid SHA1
fatal: bad revision 'HEAD'

Is this supposed to work at all?

--Imre