diff --git a/gce/jenkins-slave-windows.ps1 b/gce/jenkins-slave-windows.ps1
index 5666b6f..e5870bc 100644
--- a/gce/jenkins-slave-windows.ps1
+++ b/gce/jenkins-slave-windows.ps1
@@ -10,12 +10,26 @@
 # Install Chocolatey
 Invoke-Expression ((New-Object Net.WebClient).DownloadString("https://chocolatey.org/install.ps1"))
 
+# Initialize msys
+$msysRoot='c:\tools\msys64\'
+
+# Finally initialize and upgrade MSYS2 according to https://msys2.github.io
+Write-Host "Initializing MSYS2..."
+$msysShell = Join-Path $msysRoot msys2_shell.bat
+Start-Process -Wait $msysShell -ArgumentList '-c', exit
+
+$command = 'pacman --noconfirm --needed -Sy bash pacman pacman-mirrors msys2-runtime'
+Write-Host "Updating system packages with '$command'..."
+Start-Process -Wait $msysShell -ArgumentList '-c', "'$command'"
+
+$command = 'pacman --noconfirm -Su'
+Write-Host "Upgrading full system with '$command'..."
+Start-Process -Wait $msysShell -ArgumentList '-c', "'$command'"
+
 # Install all the Windows software we need:
-#   - msys2 because Bazel currently depends on it
-#   - JDK, because, well, Bazel is written in Java
+#   - JDK, because, Bazel is written in Java
 #   - NSSM, because that's the easiest way to create services
 #   - Chrome, because the default IE setup is way too crippled by security measures
-& choco install msys2 -y
 & choco install nssm -y
 & choco install jdk8 -y
 & choco install googlechrome -y
diff --git a/gce/vm.sh b/gce/vm.sh
index 19a8a10..48c6974 100755
--- a/gce/vm.sh
+++ b/gce/vm.sh
@@ -42,8 +42,8 @@
     "ubuntu-15-10-slave-4 https://www.googleapis.com/compute/v1/projects/ubuntu-os-cloud/global/images/ubuntu-1510-wily-v20151026 ubuntu_15.10-x86_64-4 europe-west1-c startup-script=jenkins-slave.sh ubuntu-15-10-slave.sh linux-android.sh cleanup-install.sh"
     "ubuntu-docker-slave-1 https://www.googleapis.com/compute/v1/projects/ubuntu-os-cloud/global/images/ubuntu-1510-wily-v20151026 ubuntu_15.10-x86_64-docker-1 us-east1-c startup-script=jenkins-slave.sh ubuntu-15-10-slave.sh ubuntu-15-10-docker.sh linux-android.sh cleanup-install.sh"
     # Fow Windows, we use a custom image with pre-installed MSVC.
-    "windows-slave-1 /bazel-public/windows-server-2012-r2-dc-v20160112-vs2015-cpp-python windows-x86_64-1 europe-west1-c windows-startup-script-ps1=jenkins-slave-windows.ps1"
-    "windows-slave-2 /bazel-public/windows-server-2012-r2-dc-v20160112-vs2015-cpp-python windows-x86_64-2 europe-west1-c windows-startup-script-ps1=jenkins-slave-windows.ps1"
+    "windows-slave-1 /bazel-public/windows-server-2012-r2-dc-v20160112-vs2015-cpp-python-msys windows-x86_64-1 europe-west1-c windows-startup-script-ps1=jenkins-slave-windows.ps1"
+    "windows-slave-2 /bazel-public/windows-server-2012-r2-dc-v20160112-vs2015-cpp-python-msys windows-x86_64-2 europe-west1-c windows-startup-script-ps1=jenkins-slave-windows.ps1"
 )
 
 cd "$(dirname "${BASH_SOURCE[0]}")"