diff --git a/builds/cedar-14.Dockerfile b/builds/cedar-14.Dockerfile
index 921b437..ea11542 100644
--- a/builds/cedar-14.Dockerfile
+++ b/builds/cedar-14.Dockerfile
@@ -3,7 +3,9 @@ FROM heroku/cedar:14
 WORKDIR /app
 ENV WORKSPACE_DIR="/app/builds" \
     S3_BUCKET="lang-python" \
-    S3_PREFIX="cedar-14/"
+    S3_PREFIX="cedar-14/" \
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="cedar-14"
 
 RUN apt-get update && apt-get install -y python-pip && rm -rf /var/lib/apt/lists/*
 
diff --git a/builds/heroku-16.Dockerfile b/builds/heroku-16.Dockerfile
index 0e00b3c..324042e 100644
--- a/builds/heroku-16.Dockerfile
+++ b/builds/heroku-16.Dockerfile
@@ -4,7 +4,8 @@ WORKDIR /app
 ENV WORKSPACE_DIR="/app/builds" \
     S3_BUCKET="lang-python" \
     S3_PREFIX="heroku-16/" \
-    DEBIAN_FRONTEND=noninteractive
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="heroku-16"
 
 RUN apt-get update && apt-get install -y python-pip && rm -rf /var/lib/apt/lists/*
 
diff --git a/builds/heroku-18.Dockerfile b/builds/heroku-18.Dockerfile
index b4f8239..6428fa6 100644
--- a/builds/heroku-18.Dockerfile
+++ b/builds/heroku-18.Dockerfile
@@ -4,7 +4,8 @@ WORKDIR /app
 ENV WORKSPACE_DIR="/app/builds" \
     S3_BUCKET="lang-python" \
     S3_PREFIX="heroku-18/" \
-    DEBIAN_FRONTEND=noninteractive
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="heroku-18"
 
 RUN apt-get update && apt-get install --no-install-recommends -y python-pip-whl=9.0.1-2 python-pip=9.0.1-2 python-setuptools python-wheel && rm -rf /var/lib/apt/lists/*