Invalid Priority field.

I am getting the error Invalid Priority field for the MASS package when calling packrat::init(). My MWE is as follows:

1. mkdir -p mytmpdir
2. cd mytmpdir
3. echo 'library(car)' >> script.R
4. R --no-save
5. require(packrat) && packrat::init()

I get the following:

Installing MASS (7.3-45) ...
Error: Command failed (1)

Failed to run system command:

        '/blahblah/anaconda2/envs/r-3.2.2/lib/R/bin/R' --vanilla CMD INSTALL '/tmp/RtmpOlbwQc/MASS' --library='/blahblah/mytmpdir/packrat/lib/x86_64-pc-linux-gnu/3.2.2' --install-tests --no-docs --no-multiarch --no-demo

The command failed with output:
* installing *source* package 'MASS' ...
** package 'MASS' successfully unpacked and MD5 sums checked
Error : Invalid DESCRIPTION file

Invalid Priority field.
Packages with priorities 'base' or 'recommended' or 'defunct-base' must
already be known to R.

See section 'The DESCRIPTION file' in the 'Writing R Extensions'
manual.

It seems that my installed.packages() only knows about packages with priority base or NA. This might be due to using R 3.2.2. Note that "just upgrade R" is not a feasible solution for me.

My session info:

library(packrat)
sessionInfo()

R version 3.2.2 (2015-08-14)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Red Hat Enterprise Linux Server release 6.7 (Santiago)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] packrat_0.4.8-1 fortunes_1.5-4  drat_0.1.2

loaded via a namespace (and not attached):
[1] tools_3.2.2

Run the provided MWE with R 3.2.2 and packrat::init(), then compare the package metadata reported by installed.packages() with the MASS installation failure. Read the packrat initialization and dependency-installation entry points involved in the trace. Done means MASS and other recommended packages can be initialized without requiring an R upgrade.