diff --git a/docker/launch.sh b/docker/launch.sh
index c3408b97a4..49ada09779 100755
--- a/docker/launch.sh
+++ b/docker/launch.sh
@@ -2,6 +2,14 @@
 
 set -e
 
+if [[ -z "$FORK" ]]; then
+    FORK=PowerShell
+fi
+
+if [[ -z "$BRANCH" ]]; then
+    BRANCH=master
+fi
+
 # Build both sets by default
 if [[ -z "$BUILDS" ]]; then
     BUILDS="stable unstable"
@@ -20,9 +28,10 @@ for build in $BUILDS; do
         # copy the common script because it lives outside the docker build context
         if [[ "$build" = "unstable" ]]; then
             cp bootstrap.ps1 $distro
+            buildargs="--build-arg fork=$FORK --build-arg branch=$BRANCH"
         fi
         # build and tag the image so they can be derived from
-        docker build -t powershell/powershell:$build-$distro $distro
+        docker build $buildargs -t powershell/powershell:$build-$distro $distro
     done
     cd ..
 done
diff --git a/docker/unstable/bootstrap.ps1 b/docker/unstable/bootstrap.ps1
index eda0de163b..d48c9468d3 100644
--- a/docker/unstable/bootstrap.ps1
+++ b/docker/unstable/bootstrap.ps1
@@ -1,6 +1,6 @@
 # This is intended to be used inside Docker containers
 
-git clone --recursive https://github.com/PowerShell/PowerShell.git
+git clone --recursive https://github.com/$env:fork/PowerShell.git -b $env:branch
 Set-Location PowerShell
 Import-Module ./build.psm1
 Start-PSBootstrap -Package -NoSudo
diff --git a/docker/unstable/centos7/Dockerfile b/docker/unstable/centos7/Dockerfile
index 7d4a73ac0f..0e23c90289 100644
--- a/docker/unstable/centos7/Dockerfile
+++ b/docker/unstable/centos7/Dockerfile
@@ -1,6 +1,9 @@
 FROM powershell/powershell:stable-centos7
 MAINTAINER Andrew Schwartzmeyer <andschwa@microsoft.com>
 
+ARG fork=PowerShell
+ARG branch=master
+
 COPY bootstrap.ps1 /
 RUN powershell -f bootstrap.ps1 \
     && yum install -y PowerShell/powershell*.rpm
diff --git a/docker/unstable/ubuntu14.04/Dockerfile b/docker/unstable/ubuntu14.04/Dockerfile
index 8b6b5d72c5..8754ba970b 100644
--- a/docker/unstable/ubuntu14.04/Dockerfile
+++ b/docker/unstable/ubuntu14.04/Dockerfile
@@ -1,6 +1,9 @@
 FROM powershell/powershell:stable-ubuntu14.04
 MAINTAINER Andrew Schwartzmeyer <andschwa@microsoft.com>
 
+ARG fork=PowerShell
+ARG branch=master
+
 COPY bootstrap.ps1 /
 RUN powershell -f bootstrap.ps1 \
     && dpkg -i PowerShell/powershell*.deb
diff --git a/docker/unstable/ubuntu16.04/Dockerfile b/docker/unstable/ubuntu16.04/Dockerfile
index dafb8933fe..f72cc0edfc 100644
--- a/docker/unstable/ubuntu16.04/Dockerfile
+++ b/docker/unstable/ubuntu16.04/Dockerfile
@@ -1,6 +1,9 @@
 FROM powershell/powershell:stable-ubuntu16.04
 MAINTAINER Andrew Schwartzmeyer <andschwa@microsoft.com>
 
+ARG fork=PowerShell
+ARG branch=master
+
 COPY bootstrap.ps1 /
 RUN powershell -f bootstrap.ps1 \
     && dpkg -i PowerShell/powershell*.deb