diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a6a7d7a0fe28e1355254c786b41c44b0f7bf257..f36c0a921d6b2633a9376e52d0c928f9f6df96be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Python Buildpack Changelog
 
+# 124
+
+Update buildpack to automatically install [dev-packages] (Pipenv) during Heroku CI builds.
+
 # 123
 
 Update gunicorn init.d script to allow overrides.
diff --git a/README.md b/README.md
index df808ebe5d667d2de7aea58d79a8872a438400d9..7ec68184e0f42f9a9390700ce6bb979b34a490bb 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,7 @@ Deploying a Python application couldn't be easier:
     $ git push heroku master
     …
     -----> Python app detected
-    -----> Installing python-3.6.3
+    -----> Installing python-3.6.4
     -----> Installing pip
     -----> Installing requirements with latest pipenv…
            ...
@@ -58,7 +58,7 @@ Or, more specifically:
 
 Runtime options include:
 
-- `python-3.6.3`
+- `python-3.6.4`
 - `python-2.7.14`
 - `pypy-5.7.1` (unsupported, experimental)
 - `pypy3-5.5.1` (unsupported, experimental)
diff --git a/bin/steps/pip-install b/bin/steps/pip-install
index e0d5dd391e096bfc7c605c4cf6b19d65b4bd4d6a..be92bd14d457e9b55dd1b5f6fec7646c769fe9d9 100755
--- a/bin/steps/pip-install
+++ b/bin/steps/pip-install
@@ -29,4 +29,12 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
 
     echo
+    
+    # Install test dependencies, for CI. 
+    if [ "$INSTALL_TEST" ]; then
+        if [[ -f "$1/requirements-test.txt" ]]; then
+            puts-step "Installing test dependencies…"
+            /app/.heroku/python/bin/pip install -r "$1/requirements-test.txt" --exists-action=w --src=./.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | cleanup | indent
+        fi
+    fi
 fi
diff --git a/bin/steps/pipenv b/bin/steps/pipenv
index 857bcd82890a8a02832d989ca0d271838b0ef98a..5e050f740938ac88539ae485ed49d04682fac2d5 100644
--- a/bin/steps/pipenv
+++ b/bin/steps/pipenv
@@ -16,13 +16,18 @@ if [[ -f Pipfile ]]; then
         # Install pipenv.
         /app/.heroku/python/bin/pip install pipenv --upgrade &> /dev/null
 
+        # Install the dependencies.
         if [[ ! -f Pipfile.lock ]]; then
             /app/.heroku/python/bin/pipenv install --system --skip-lock 2>&1 | indent
         else
             /app/.heroku/python/bin/pipenv install --system --deploy 2>&1 | indent
         fi
-        # Install the dependencies.
 
+        # Install the test dependencies, for CI.
+        if [ "$INSTALL_TEST" ]; then
+            puts-step "Installing test dependencies…"
+            /app/.heroku/python/bin/pipenv install --dev --system --deploy 2>&1 | cleanup | indent
+        fi
 
         # Skip pip install, later.
         export SKIP_PIP_INSTALL=1
diff --git a/bin/test-compile b/bin/test-compile
index d19814dbbe6bd55413a972fd0ed711ed89bc2c57..fa4a6580a3e7eb2158165f47cc46f37ee1d5e6b2 100755
--- a/bin/test-compile
+++ b/bin/test-compile
@@ -6,8 +6,8 @@ BIN_DIR=$(cd "$(dirname "$0")" || return; pwd) # absolute path
 # shellcheck source=bin/utils
 source "$BIN_DIR/utils"
 
-DISABLE_COLLECTSTATIC=1 "$(dirname "${0:-}")/compile" "$1" "$2" "$3"
+# Locale support for Pipenv.
+export LC_ALL=C.UTF-8
+export LANG=C.UTF-8
 
-if [[ -f "$1/requirements-test.txt" ]]; then
-    /app/.heroku/python/bin/pip install -r "$1/requirements-test.txt" --exists-action=w --src=./.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | cleanup | indent
-fi
+DISABLE_COLLECTSTATIC=1 INSTALL_TEST=1 "$(dirname "${0:-}")/compile" "$1" "$2" "$3"
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