diff --git a/taskcluster/ci/test/compiled.yml b/taskcluster/ci/test/compiled.yml
index 4bd462932bb0..aa4e80374700 100644
--- a/taskcluster/ci/test/compiled.yml
+++ b/taskcluster/ci/test/compiled.yml
@@ -30,6 +30,7 @@ job-defaults:
                     - unittests/mac_unittest.py
                 windows.*:
                     - unittests/win_unittest.py
+    python-3: true
 
 cppunit:
     description: "CPP Unit Tests"
diff --git a/testing/mozharness/configs/raptor/windows_config.py b/testing/mozharness/configs/raptor/windows_config.py
index 7b0e56f77bf3..4554e9919034 100644
--- a/testing/mozharness/configs/raptor/windows_config.py
+++ b/testing/mozharness/configs/raptor/windows_config.py
@@ -11,11 +11,15 @@ PYTHON = sys.executable
 PYTHON_DLL = "c:/mozilla-build/python27/python27.dll"
 VENV_PATH = os.path.join(os.getcwd(), "build/venv")
 
+PYWIN32 = "pypiwin32==219"
+if sys.version_info > (3, 0):
+    PYWIN32 = "pywin32==300"
+
 config = {
     "log_name": "raptor",
     "installer_path": "installer.exe",
     "virtualenv_path": VENV_PATH,
-    "virtualenv_modules": ["pypiwin32==219", "raptor", "mozinstall"],
+    "virtualenv_modules": [PYWIN32, "raptor", "mozinstall"],
     "exes": {
         "python": PYTHON,
         "easy_install": [
diff --git a/testing/mozharness/configs/raptor/windows_vm_config.py b/testing/mozharness/configs/raptor/windows_vm_config.py
index 0ab677a79405..b68697feed72 100644
--- a/testing/mozharness/configs/raptor/windows_vm_config.py
+++ b/testing/mozharness/configs/raptor/windows_vm_config.py
@@ -11,11 +11,15 @@ PYTHON = sys.executable
 PYTHON_DLL = "c:/mozilla-build/python27/python27.dll"
 VENV_PATH = os.path.join(os.getcwd(), "build/venv")
 
+PYWIN32 = "pypiwin32==219"
+if sys.version_info > (3, 0):
+    PYWIN32 = "pywin32==300"
+
 config = {
     "log_name": "raptor",
     "installer_path": "installer.exe",
     "virtualenv_path": VENV_PATH,
-    "virtualenv_modules": ["pypiwin32==219", "raptor", "mozinstall"],
+    "virtualenv_modules": [PYWIN32, "raptor", "mozinstall"],
     "exes": {
         "python": PYTHON,
         "easy_install": [
diff --git a/testing/mozharness/configs/unittests/win_unittest.py b/testing/mozharness/configs/unittests/win_unittest.py
index e5849c456c80..30e069913a8b 100644
--- a/testing/mozharness/configs/unittests/win_unittest.py
+++ b/testing/mozharness/configs/unittests/win_unittest.py
@@ -15,6 +15,10 @@ NODEJS_PATH = None
 if "MOZ_FETCHES_DIR" in os.environ:
     NODEJS_PATH = os.path.join(os.environ["MOZ_FETCHES_DIR"], "node/node.exe")
 
+PYWIN32 = "pypiwin32==219"
+if sys.version_info > (3, 0):
+    PYWIN32 = "pywin32==300"
+
 XPCSHELL_NAME = "xpcshell.exe"
 EXE_SUFFIX = ".exe"
 DISABLE_SCREEN_SAVER = False
@@ -39,7 +43,7 @@ config = {
     "installer_path": INSTALLER_PATH,
     "binary_path": BINARY_PATH,
     "xpcshell_name": XPCSHELL_NAME,
-    "virtualenv_modules": ["pypiwin32==219", "six==1.13.0", "vcversioner==2.16.0.0"],
+    "virtualenv_modules": [PYWIN32, "six==1.13.0", "vcversioner==2.16.0.0"],
     "virtualenv_path": "venv",
     "exe_suffix": EXE_SUFFIX,
     "run_file_names": {
diff --git a/testing/remotecppunittests.py b/testing/remotecppunittests.py
index c486112f89a6..03748aaf3531 100644
--- a/testing/remotecppunittests.py
+++ b/testing/remotecppunittests.py
@@ -64,7 +64,7 @@ class RemoteCPPUnitTests(cppunittests.CPPUnitTests):
                         )
                         apk_contents.extract(info, tmpdir)
                         local_file = os.path.join(tmpdir, info.filename)
-                        with open(local_file) as f:
+                        with open(local_file, "rb") as f:
                             # Decompress xz-compressed file.
                             if f.read(5)[1:] == "7zXZ":
                                 cmd = ["xz", "-df", "--suffix", ".so", local_file]