diff --git a/Lib/ensurepip/__init__.py b/Lib/ensurepip/__init__.py
--- a/Lib/ensurepip/__init__.py
+++ b/Lib/ensurepip/__init__.py
@@ -58,6 +58,12 @@
     # See http://bugs.python.org/issue20053 for details
     os.environ['PIP_CONFIG_FILE'] = os.devnull
 
+def _ensure_streams():
+    # pip requires sys.__stdout__ to be set, which normally prevents
+    # installing it with pythonw.exe on Windows.
+    if not sys.__stdout__:
+        import io
+        sys.stdout = sys.__stdout__ = io.TextIOWrapper(io.BytesIO())
 
 def bootstrap(*, root=None, upgrade=False, user=False,
               altinstall=False, default_pip=False,
@@ -73,6 +79,7 @@
 
     _require_ssl_for_pip()
     _disable_pip_configuration_settings()
+    _ensure_streams()
 
     # By default, installing pip and setuptools installs all of the
     # following scripts (X.Y == running Python version):
diff --git a/Lib/ensurepip/_uninstall.py b/Lib/ensurepip/_uninstall.py
--- a/Lib/ensurepip/_uninstall.py
+++ b/Lib/ensurepip/_uninstall.py
@@ -23,6 +23,7 @@
 
     args = parser.parse_args(argv)
 
+    ensurepip._ensure_streams()
     ensurepip._uninstall_helper(verbosity=args.verbosity)