diff --git a/src/python/grpcio_tests/tests/_runner.py b/src/python/grpcio_tests/tests/_runner.py
index 39da0399b02..06f5d88fc3d 100644
--- a/src/python/grpcio_tests/tests/_runner.py
+++ b/src/python/grpcio_tests/tests/_runner.py
@@ -59,7 +59,7 @@ class CaptureFile(object):
         """Get all output from the redirected-to file if it exists."""
         if self._into_file:
             self._into_file.seek(0)
-            return bytes(self._into_file.read())
+            return bytes(self._into_file.read(), 'ascii')
         else:
             return bytes()
 
diff --git a/tools/run_tests/python_utils/port_server.py b/tools/run_tests/python_utils/port_server.py
index 256611c5aef..7c89929aab0 100755
--- a/tools/run_tests/python_utils/port_server.py
+++ b/tools/run_tests/python_utils/port_server.py
@@ -157,7 +157,7 @@ class Handler(BaseHTTPRequestHandler):
             self.end_headers()
             p = allocate_port(self)
             self.log_message('allocated port %d' % p)
-            self.wfile.write(bytes('%d' % p))
+            self.wfile.write(('%d' % p).encode('utf8'))
         elif self.path[0:6] == '/drop/':
             self.send_response(200)
             self.send_header('Content-Type', 'text/plain')
@@ -177,7 +177,7 @@ class Handler(BaseHTTPRequestHandler):
             self.send_response(200)
             self.send_header('Content-Type', 'text/plain')
             self.end_headers()
-            self.wfile.write(bytes('%d' % _MY_VERSION))
+            self.wfile.write(bytes('%d' % _MY_VERSION, 'ascii'))
         elif self.path == '/dump':
             # yaml module is not installed on Macs and Windows machines by default
             # so we import it lazily (/dump action is only used for debugging)
@@ -192,7 +192,7 @@ class Handler(BaseHTTPRequestHandler):
                 'in_use': dict((k, now - v) for k, v in in_use.items())
             })
             mu.release()
-            self.wfile.write(bytes(out))
+            self.wfile.write(bytes(out, 'ascii'))
         elif self.path == '/quitquitquit':
             self.send_response(200)
             self.end_headers()