diff --git a/trezorlib/client.py b/trezorlib/client.py
index d3281be..e921477 100644
--- a/trezorlib/client.py
+++ b/trezorlib/client.py
@@ -632,7 +632,7 @@ class ProtocolMixin(object):
     def sign_message(self, coin_name, n, message, script_type=proto.InputScriptType.SPENDADDRESS):
         n = self._convert_prime(n)
         # Convert message to UTF8 NFC (seems to be a bitcoin-qt standard)
-        message = normalize_nfc(message).encode("utf-8")
+        message = normalize_nfc(message).encode('utf-8')
         return self.call(proto.SignMessage(coin_name=coin_name, address_n=n, message=message, script_type=script_type))
 
     @expect(proto.SignedIdentity)
@@ -786,7 +786,7 @@ class ProtocolMixin(object):
 
     def verify_message(self, coin_name, address, signature, message):
         # Convert message to UTF8 NFC (seems to be a bitcoin-qt standard)
-        message = normalize_nfc(message).encode("utf-8")
+        message = normalize_nfc(message).encode('utf-8')
         try:
             resp = self.call(proto.VerifyMessage(address=address, signature=signature, message=message, coin_name=coin_name))
         except CallException as e:
diff --git a/trezorlib/protobuf.py b/trezorlib/protobuf.py
index 4237610..da6cdc2 100644
--- a/trezorlib/protobuf.py
+++ b/trezorlib/protobuf.py
@@ -290,7 +290,7 @@ def dump_message(writer, msg):
 
             elif ftype is UnicodeType:
                 if not isinstance(svalue, bytes):
-                    svalue = svalue.encode()
+                    svalue = svalue.encode('utf-8')
 
                 dump_uvarint(writer, len(svalue))
                 writer.write(svalue)