diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h b/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
index 02b90bbf4..1a25e39a0 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
@@ -70,7 +70,7 @@ STATIC mp_obj_t mod_TrezorCrypto_Nist256p1_sign(size_t n_args, const mp_obj_t *a
     mp_buffer_info_t sk, dig;
     mp_get_buffer_raise(args[1], &sk, MP_BUFFER_READ);
     mp_get_buffer_raise(args[2], &dig, MP_BUFFER_READ);
-    bool compressed = n_args > 3 && args[3] == mp_const_true;
+    bool compressed = n_args < 4 || args[3] == mp_const_true;
     if (sk.len != 32) {
         mp_raise_ValueError("Invalid length of secret key");
     }
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h b/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
index 3f8ed2412..5205c7dc0 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
@@ -70,7 +70,7 @@ STATIC mp_obj_t mod_TrezorCrypto_Secp256k1_sign(size_t n_args, const mp_obj_t *a
     mp_buffer_info_t sk, dig;
     mp_get_buffer_raise(args[1], &sk, MP_BUFFER_READ);
     mp_get_buffer_raise(args[2], &dig, MP_BUFFER_READ);
-    bool compressed = n_args > 3 && args[3] == mp_const_true;
+    bool compressed = n_args < 4 || args[3] == mp_const_true;
     if (sk.len != 32) {
         mp_raise_ValueError("Invalid length of secret key");
     }
diff --git a/src/apps/wallet/layout_sign_message.py b/src/apps/wallet/layout_sign_message.py
index 3ea036009..b641cc525 100644
--- a/src/apps/wallet/layout_sign_message.py
+++ b/src/apps/wallet/layout_sign_message.py
@@ -3,14 +3,37 @@ from trezor.utils import unimport
 
 
 @unimport
-async def layout_sign_message(message, session_id):
-    from trezor.messages.Success import Success
+async def layout_sign_message(msg, session_id):
+    from trezor.messages.MessageSignature import MessageSignature
+    from trezor.crypto.hashlib import sha256
+    from trezor.crypto.curve import secp256k1
+    from ..common.signtx import node_derive, HashWriter, write_varint
+    from ..common.seed import get_root_node
+    from ..common import coins
 
     ui.display.clear()
     ui.display.text(10, 30, 'Signing message',
                     ui.BOLD, ui.LIGHT_GREEN, ui.BLACK)
-    ui.display.text(10, 60, message.message, ui.MONO, ui.WHITE, ui.BLACK)
+    ui.display.text(10, 60, msg.message, ui.MONO, ui.WHITE, ui.BLACK)
 
-    # TODO
+    address_n = msg.address_n
+    message = msg.message
+    coin_name = getattr(msg, 'coin_name', 'Bitcoin')
+    coin = coins.by_name(coin_name)
 
-    return Success(message='Signed')
+    root = await get_root_node(session_id)
+    node = node_derive(root, address_n)
+    seckey = node.private_key()
+    address = node.address(coin.address_type)
+
+    h = HashWriter(sha256)
+    write_varint(h, len(coin.signed_message_header))
+    h.extend(coin.signed_message_header)
+    write_varint(h, len(message))
+    h.extend(message)
+
+    digest = sha256(h.getvalue()).digest()
+
+    signature = secp256k1.sign(seckey, digest)
+
+    return MessageSignature(address=address, signature=signature)