diff --git a/Dockerfile b/Dockerfile
index 82758daf..124f68cd 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,6 @@
-FROM python:2.7
+ARG PYTHON_VERSION=2.7
+
+FROM python:${PYTHON_VERSION}
 
 RUN mkdir /src
 WORKDIR /src
diff --git a/Dockerfile-docs b/Dockerfile-docs
index 105083e8..9d11312f 100644
--- a/Dockerfile-docs
+++ b/Dockerfile-docs
@@ -1,4 +1,6 @@
-FROM python:3.5
+ARG PYTHON_VERSION=3.7
+
+FROM python:${PYTHON_VERSION}
 
 ARG uid=1000
 ARG gid=1000
diff --git a/Dockerfile-py3 b/Dockerfile-py3
index d558ba3e..22732dec 100644
--- a/Dockerfile-py3
+++ b/Dockerfile-py3
@@ -1,4 +1,6 @@
-FROM python:3.6
+ARG PYTHON_VERSION=3.7
+
+FROM python:${PYTHON_VERSION}
 
 RUN mkdir /src
 WORKDIR /src
diff --git a/tests/Dockerfile b/tests/Dockerfile
index 8f49cd2c..f2f36b44 100644
--- a/tests/Dockerfile
+++ b/tests/Dockerfile
@@ -1,5 +1,6 @@
-ARG PYTHON_VERSION=3.6
-FROM python:$PYTHON_VERSION-jessie
+ARG PYTHON_VERSION=3.7
+
+FROM python:${PYTHON_VERSION}
 RUN apt-get update && apt-get -y install \
     gnupg2 \
     pass \
@@ -8,7 +9,7 @@ RUN apt-get update && apt-get -y install \
 COPY ./tests/gpg-keys /gpg-keys
 RUN gpg2 --import gpg-keys/secret
 RUN gpg2 --import-ownertrust gpg-keys/ownertrust
-RUN yes | pass init $(gpg2 --no-auto-check-trustdb --list-secret-keys | grep ^sec | cut -d/ -f2 | cut -d" " -f1)
+RUN yes | pass init $(gpg2 --no-auto-check-trustdb --list-secret-key | awk '/^sec/{getline; $1=$1; print}')
 RUN gpg2 --check-trustdb
 ARG CREDSTORE_VERSION=v0.6.2
 RUN curl -sSL -o /opt/docker-credential-pass.tar.gz \
diff --git a/tests/Dockerfile-dind-certs b/tests/Dockerfile-dind-certs
index 9e8c042b..2ab87ef7 100644
--- a/tests/Dockerfile-dind-certs
+++ b/tests/Dockerfile-dind-certs
@@ -1,4 +1,6 @@
-FROM python:2.7
+ARG PYTHON_VERSION=2.7
+
+FROM python:${PYTHON_VERSION}
 RUN mkdir /tmp/certs
 VOLUME /certs