diff --git a/taskcluster/ci/openh264-plugin/kind.yml b/taskcluster/ci/openh264-plugin/kind.yml
index 23e12c71ddee..a434ad2c6caa 100644
--- a/taskcluster/ci/openh264-plugin/kind.yml
+++ b/taskcluster/ci/openh264-plugin/kind.yml
@@ -130,6 +130,26 @@ jobs:
                 - openh264/win64.py
         toolchains:
             - win64-clang-cl
+    win64-aarch64/opt:
+        attributes:
+            build_platform: windows2012-aarch64
+            build_type: opt
+        treeherder:
+            platform: win64-aarch64/opt
+        worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
+        worker:
+            max-run-time: 1800
+            artifacts:
+                - name: private/openh264
+                  path: build/openh264/artifacts
+                  type: directory
+        run:
+            using: mozharness
+            script: mozharness/scripts/openh264_build.py
+            config:
+                - openh264/win64-aarch64.py
+        toolchains:
+            - win64-clang-cl
     android-api-16/opt:
         attributes:
             build_platform: android-arm
diff --git a/testing/mozharness/configs/openh264/tooltool-manifests/win64-aarch64.manifest b/testing/mozharness/configs/openh264/tooltool-manifests/win64-aarch64.manifest
new file mode 100644
index 000000000000..0502193a1a8d
--- /dev/null
+++ b/testing/mozharness/configs/openh264/tooltool-manifests/win64-aarch64.manifest
@@ -0,0 +1,18 @@
+[
+  {
+    "size": 56832,
+    "visibility": "public",
+    "digest": "01e6bd936ef008061b95a94008682869ebf2a29d1c035e49cd6579b1a020d0d195431221577f127eb52b97137337efe30e6de6c5a2f4b6a87ff2a990e9874e8e",
+    "algorithm": "sha512",
+    "filename": "dump_syms.exe"
+  },
+  {
+    "version": "Visual Studio 2017 15.9.6 / SDK 10.0.17134.0",
+    "size": 490015895,
+    "visibility": "internal",
+    "digest": "91d08703a8ce39f6f53ccecc7c7b6f57e1b571ddb5d1eb4dd9260e52580566c35a4bed39ad366fd60ca60ebf5c06f0f00561bba5cd631826511f2872a3d2dcd5",
+    "algorithm": "sha512",
+    "filename": "vs2017_15.9.6.zip",
+    "unpack": true
+  }
+]
diff --git a/testing/mozharness/configs/openh264/win64-aarch64.py b/testing/mozharness/configs/openh264/win64-aarch64.py
new file mode 100644
index 000000000000..f4ce087b9b29
--- /dev/null
+++ b/testing/mozharness/configs/openh264/win64-aarch64.py
@@ -0,0 +1,46 @@
+import sys
+import os
+
+import mozharness
+
+external_tools_path = os.path.join(
+    os.path.abspath(os.path.dirname(os.path.dirname(mozharness.__file__))),
+    'external_tools',
+)
+
+VSPATH = '%(abs_work_dir)s\\src\\vs2017_15.9.6'
+config = {
+    'tooltool_manifest_file': 'win64-aarch64.manifest',
+    'exes': {
+        'gittool.py': [sys.executable, os.path.join(external_tools_path, 'gittool.py')],
+        'python2.7': 'c:\\mozilla-build\\python\\python.exe',
+    },
+    'dump_syms_binary': 'dump_syms.exe',
+    'arch': 'aarch64',
+    'use_yasm': False,
+    'partial_env': {
+        'PATH': ('%(abs_work_dir)s\\openh264;'
+                 '%(abs_work_dir)s\\src\\clang\\bin\\;'
+                 '{_VSPATH}\\VC\\bin\\Hostx64\\arm64;'
+                 '{_VSPATH}\\VC\\bin\\Hostx64\\x64;'
+                 # 32-bit redist here for our dump_syms.exe
+                 '{_VSPATH}/VC/redist/x86/Microsoft.VC141.CRT;'
+                 '{_VSPATH}/SDK/Redist/ucrt/DLLs/x86;'
+                 '{_VSPATH}/DIA SDK/bin;%(PATH)s;'
+        ).format(_VSPATH=VSPATH),
+        'INCLUDES': (
+            '-I{_VSPATH}\\VC\\include '
+            '-I{_VSPATH}\\VC\\atlmfc\\include '
+            '-I{_VSPATH}\\SDK\\Include\\10.0.17134.0\\ucrt '
+            '-I{_VSPATH}\\SDK\\Include\\10.0.17134.0\\shared '
+            '-I{_VSPATH}\\SDK\\Include\\10.0.17134.0\\um '
+            '-I{_VSPATH}\\SDK\\Include\\10.0.17134.0\\winrt '
+        ).format(_VSPATH=VSPATH),
+        'LIB': (
+            '{_VSPATH}/VC/lib/arm64;'
+            '{_VSPATH}/VC/atlmfc/lib/arm64;'
+            '{_VSPATH}/SDK/lib/10.0.17134.0/ucrt/arm64;'
+            '{_VSPATH}/SDK/lib/10.0.17134.0/um/arm64;'
+        ).format(_VSPATH=VSPATH),
+    },
+}
diff --git a/testing/mozharness/scripts/openh264_build.py b/testing/mozharness/scripts/openh264_build.py
index a6be9891c548..3e2af4d52770 100755
--- a/testing/mozharness/scripts/openh264_build.py
+++ b/testing/mozharness/scripts/openh264_build.py
@@ -149,7 +149,7 @@ class OpenH264Build(TransferMixin, VCSScript, TooltoolMixin):
             self.error('missing a required key.')
 
     def query_package_name(self):
-        if self.config['arch'] == "x64":
+        if self.config['arch'] == 'x64':
             bits = '64'
         else:
             bits = '32'
@@ -164,10 +164,13 @@ class OpenH264Build(TransferMixin, VCSScript, TooltoolMixin):
                     version=version, bits=bits)
             else:
                 return 'openh264-linux{bits}-{version}.zip'.format(version=version, bits=bits)
-        elif sys.platform == 'darwin':
-            return 'openh264-macosx{bits}-{version}.zip'.format(version=version, bits=bits)
         elif sys.platform == 'win32':
-            return 'openh264-win{bits}-{version}.zip'.format(version=version, bits=bits)
+            if self.config['arch'] == 'aarch64':
+                return 'openh264-win64-aarch64-{version}.zip'.format(
+                    version=version)
+            else:
+                return 'openh264-win{bits}-{version}.zip'.format(
+                    version=version, bits=bits)
         self.fatal("can't determine platform")
 
     def query_make_params(self):
@@ -210,6 +213,10 @@ class OpenH264Build(TransferMixin, VCSScript, TooltoolMixin):
             if self.config['arch'] == 'x86':
                 retval.append("ARCH=x86")
                 retval.append("CFLAGS=-m32")
+            elif self.config['arch'] == 'aarch64':
+                retval.append("ARCH=arm64")
+                retval.append("CFLAGS=--target=aarch64-windows-msvc")
+                retval.append("CXX_LINK_O=-nologo --target=aarch64-windows-msvc -Fe$@")
             else:
                 retval.append("ARCH=x86_64")
         else:
@@ -263,6 +270,24 @@ class OpenH264Build(TransferMixin, VCSScript, TooltoolMixin):
             self.copytree(os.path.join(dirs['abs_work_dir'], 'src', 'dom',
                                        'media', 'gmp', 'gmp-api'),
                           os.path.join(repo_dir, 'gmp-api'))
+
+            # We need gas-preprocessor.pl for arm64 builds
+            if self.config['arch'] == 'aarch64':
+                openh264_dir = os.path.join(dirs['abs_work_dir'], 'openh264')
+                self.download_file(('https://raw.githubusercontent.com/libav/'
+                                    'gas-preprocessor/c2bc63c96678d9739509e58'
+                                    '7aa30c94bdc0e636d/gas-preprocessor.pl'),
+                                   parent_dir=openh264_dir)
+                self.chmod(os.path.join(openh264_dir, 'gas-preprocessor.pl'),
+                           744)
+
+                # gas-preprocessor.pl expects cpp to exist
+                # os.symlink is not available on Windows until we switch to
+                # Python 3.
+                os.system('ln -s %s %s' % (
+                          os.path.join(dirs['abs_work_dir'], 'src', 'clang',
+                                       'bin', 'clang.exe'),
+                          os.path.join(openh264_dir, 'cpp')))
             return 0
 
         repos = [