postmaster became multithreaded during startup

Hi, all,

I am experiencing a startup failure on OS X 10.11.3, with PostgreSQL 9.5.1 that I installed using Homebrew.

Here's the full error:

$ postgres -d 5 -D db
DEBUG: postgres: PostmasterMain: initial environment dump:
DEBUG: -----------------------------------------
DEBUG: TERM_PROGRAM=iTerm.app
DEBUG: SHELL=/bin/bash
DEBUG: TERM=xterm-256color
DEBUG: TMPDIR=/var/folders/3r/vzj1r6_918qghdqk517g55bcg3gy47/T/
DEBUG: Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.39PGlvUVAG/Render
DEBUG: USER=pmw
DEBUG: SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.QFbewTSIsA/Listeners
DEBUG: __CF_USER_TEXT_ENCODING=0x1E37F887:0x0:0x0
DEBUG: PATH=/Users/pmw/.rbenv/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
DEBUG: PWD=/Users/pmw/my-data
DEBUG: JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_74.jdk/Contents/Home
DEBUG: LANG=en_US.UTF-8
DEBUG: MEMDEF_POLICY=CCCCCCCCCCCCCAAAAAAAACC:C
DEBUG: ITERM_PROFILE=Default
DEBUG: XPC_FLAGS=0x0
DEBUG: XPC_SERVICE_NAME=0
DEBUG: SHLVL=1
DEBUG: COLORFGBG=7;0
DEBUG: HOME=/Users/pmw
DEBUG: ITERM_SESSION_ID=w0t0p0
DEBUG: LOGNAME=pmw
DEBUG: _=/usr/local/bin/postgres
DEBUG: OLDPWD=/Users/pmw
DEBUG: PGSYSCONFDIR=/usr/local/etc/postgresql
DEBUG: LC_COLLATE=en_US.UTF-8
DEBUG: LC_CTYPE=en_US.UTF-8
DEBUG: LC_MESSAGES=en_US.UTF-8
DEBUG: LC_MONETARY=C
DEBUG: LC_NUMERIC=C
DEBUG: LC_TIME=C
DEBUG: -----------------------------------------
DEBUG: invoking IpcMemoryCreate(size=148488192)
DEBUG: SlruScanDirectory invoking callback on pg_notify/0000
DEBUG: removing file "pg_notify/0000"
DEBUG: dynamic shared memory system will support 288 segments
DEBUG: created dynamic shared memory control segment 1804289383 (2316 bytes)
DEBUG: max_safe_fds = 982, usable_fds = 1000, already_open = 8
FATAL: postmaster became multithreaded during startup
HINT: Set the LC_ALL environment variable to a valid locale.
DEBUG: shmem_exit(1): 0 before_shmem_exit callbacks to make
DEBUG: shmem_exit(1): 4 on_shmem_exit callbacks to make
DEBUG: cleaning up dynamic shared memory control segment with ID 1804289383
DEBUG: proc_exit(1): 2 callbacks to make
DEBUG: exit(1)
DEBUG: shmem_exit(-1): 0 before_shmem_exit callbacks to make
DEBUG: shmem_exit(-1): 0 on_shmem_exit callbacks to make
DEBUG: proc_exit(-1): 0 callbacks to make

$ locale
LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

Now that my LC_* variables are correct, I am stumped. Any ideas?

--
Philip