diff --git a/diskimage_builder/elements/gentoo/README.rst b/diskimage_builder/elements/gentoo/README.rst
index ca11c6522..8c7dcdde7 100644
--- a/diskimage_builder/elements/gentoo/README.rst
+++ b/diskimage_builder/elements/gentoo/README.rst
@@ -31,9 +31,9 @@ Notes:
     default/linux/amd64/17.0/hardened
     default/linux/amd64/17.0/no-multilib/hardened
 
-* You can set the GENTOO_PORTAGE_CLEANUP environment variable to true (or
-  anything other than False) to clean up portage from the system and get the
-  image size smaller.
+* You can set the GENTOO_PORTAGE_CLEANUP environment variable to False to
+  prevent cleaning up portage repositories (including overlays).  This makes
+  the image bigger.
 
 * Gentoo supports many diferent versions of python, in order to select one
   you may use the `GENTOO_PYTHON_TARGETS` environment variable to select
diff --git a/diskimage_builder/elements/gentoo/environment.d/00-gentoo-envars.bash b/diskimage_builder/elements/gentoo/environment.d/00-gentoo-envars.bash
index f423394e9..3b55eab57 100644
--- a/diskimage_builder/elements/gentoo/environment.d/00-gentoo-envars.bash
+++ b/diskimage_builder/elements/gentoo/environment.d/00-gentoo-envars.bash
@@ -1,7 +1,7 @@
 export DIB_RELEASE=gentoo
 export DISTRO_NAME=gentoo
 export GENTOO_PROFILE=${GENTOO_PROFILE:-'default/linux/amd64/17.0'}
-export GENTOO_PORTAGE_CLEANUP=${GENTOO_PORTAGE_CLEANUP:-'False'}
+export GENTOO_PORTAGE_CLEANUP=${GENTOO_PORTAGE_CLEANUP:-'True'}
 export GENTOO_PYTHON_TARGETS=${GENTOO_PYTHON_TARGETS:-'python2_7 python3_5'}
 export GENTOO_PYTHON_ACTIVE_VERSION=${GENTOO_PYTHON_ACTIVE_VERSION:-'python3.5'}
 export GENTOO_OVERLAYS=${GENTOO_OVERLAYS:-''}