diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index df29187b46d..327d3b3646a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,6 +1,13 @@
 name: CI
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || format('{0}-{1}', github.ref, github.run_number) }}
@@ -9,7 +16,9 @@ concurrency:
 jobs:
   # CI matrix - runs the job in lagom-template.yml with different configurations.
   Lagom:
-    if: github.repository == 'LadybirdBrowser/ladybird'
+    if: |
+      github.repository == 'LadybirdBrowser/ladybird'
+      && (github.event_name != 'pull_request' || github.event.action != 'labeled' || github.event.label.name == 'windows')
     name: ${{ matrix.os_name }}, ${{ matrix.arch }}, ${{ matrix.build_preset }}, ${{ matrix.toolchain }}
 
     strategy:
@@ -44,6 +53,17 @@ jobs:
             clang_plugins: false
             runner_labels: '["blacksmith-16vcpu-ubuntu-2404"]'
 
+          - os_name: 'Windows'
+            arch: 'x86_64'
+            build_preset: 'Windows_Sanitizer_CI'
+            toolchain: 'ClangCL'
+            clang_plugins: false
+            runner_labels: '["windows-2025"]'
+
+        exclude:
+          # Exclude the Windows build from the matrix if the PR is not labeled with 'windows'.
+          - os_name: ${{ !contains(github.event.pull_request.labels.*.name, 'windows') && 'Windows' }}
+
     uses: ./.github/workflows/lagom-template.yml
     with:
       toolchain: ${{ matrix.toolchain }}