diff --git a/elements/pypi/README.md b/elements/pypi/README.md
index 10002fd2d..f83ffc491 100644
--- a/elements/pypi/README.md
+++ b/elements/pypi/README.md
@@ -1,13 +1,15 @@
 Inject a PyPI mirror
 ====================
 
-Bind mounts a PyPI mirror from ~/.cache/image-create/pypi/mirror into the build
-environment and temporarily overwrites /root/.pip.conf and .pydistutils.cfg to
-use it.
+Use a custom PyPI mirror to build images. The default is to bind mount one from
+~/.cache/image-create/pypi/mirror into the build environment. The element
+temporarily overwrites /root/.pip.conf and .pydistutils.cfg to use it.
 
-When online, the master pypi index is supplied as an extra-url, so uncached
-dependencies will still be available. When offline, only the mirror is used - a
-stale mirror will cause build failures.
+When online, the official pypi.python.org pypi index is supplied as an
+extra-url, so uncached dependencies will still be available. When offline, only
+the mirror is used - be warned that a stale mirror will cause build failures.
+
+To use an arbitrary mirror set PYPI\_MIRROR\_URL=http[s]://somevalue/
 
 [jeepyb](https://git.openstack.org/cgit/openstack-infra/jeepyb) can be useful in making a
 partial PyPI mirror suitable for building images. For instance:
diff --git a/elements/pypi/extra-data.d/00-mount-pypi-mirror b/elements/pypi/extra-data.d/00-mount-pypi-mirror
index 8aa01611e..6cc12534b 100755
--- a/elements/pypi/extra-data.d/00-mount-pypi-mirror
+++ b/elements/pypi/extra-data.d/00-mount-pypi-mirror
@@ -2,6 +2,11 @@
 
 set -eu
 
+PYPI_MIRROR_URL=${PYPI_MIRROR_URL:-''}
+if [ -n "$PYPI_MIRROR_URL" ]; then
+  # External mirror URL being used - no need to bind mount anything.
+  exit 0
+fi
 MIRROR_SOURCE=~/.cache/image-create/pypi/mirror/
 MIRROR_TARGET=$TMP_MOUNT_PATH/tmp/pypi
 
diff --git a/elements/pypi/pre-install.d/00-configure-pypi-mirror b/elements/pypi/pre-install.d/00-configure-pypi-mirror
index 402951c51..89c48ec3a 100755
--- a/elements/pypi/pre-install.d/00-configure-pypi-mirror
+++ b/elements/pypi/pre-install.d/00-configure-pypi-mirror
@@ -2,7 +2,7 @@
 
 set -eu
 
-PYPIURL=file:///tmp/pypi
+PYPIURL=${PYPI_MIRROR_URL:-'file:///tmp/pypi'}
 mkdir -p ~/.pip
 
 if [ -e ~/.pip/pip.conf ]; then