diff --git a/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2b.h b/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2b.h
index 27e1fb23c0..a686508a32 100644
--- a/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2b.h
+++ b/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2b.h
@@ -33,21 +33,29 @@ typedef struct _mp_obj_Blake2b_t {
 
 STATIC mp_obj_t mod_trezorcrypto_Blake2b_update(mp_obj_t self, mp_obj_t data);
 
-/// def __init__(self, data: bytes = None, key: bytes = None) -> None:
+/// def __init__(self, data: bytes = None, outlen: int = Blake2b.digest_size, key: bytes = None) -> None:
 ///     '''
 ///     Creates a hash context object.
 ///     '''
 STATIC mp_obj_t mod_trezorcrypto_Blake2b_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
-    mp_arg_check_num(n_args, n_kw, 0, 2, false);
+    mp_arg_check_num(n_args, n_kw, 0, 3, false);
     mp_obj_Blake2b_t *o = m_new_obj(mp_obj_Blake2b_t);
     o->base.type = type;
+    int res = 0;
     // constructor called with key argument set
-    if (n_args == 2) {
+    if (n_args == 3) {
+        size_t outlen = mp_obj_get_int(args[1]);
         mp_buffer_info_t key;
-        mp_get_buffer_raise(args[1], &key, MP_BUFFER_READ);
-        blake2b_InitKey(&(o->ctx), BLAKE2B_DIGEST_LENGTH, key.buf, key.len);
+        mp_get_buffer_raise(args[2], &key, MP_BUFFER_READ);
+        res = blake2b_InitKey(&(o->ctx), outlen, key.buf, key.len);
+    } else if (n_args == 2) {
+        size_t outlen = mp_obj_get_int(args[1]);
+        res = blake2b_Init(&(o->ctx), outlen);
     } else {
-        blake2b_Init(&(o->ctx), BLAKE2B_DIGEST_LENGTH);
+        res = blake2b_Init(&(o->ctx), BLAKE2B_DIGEST_LENGTH);
+    }
+    if (res < 0) {
+        mp_raise_ValueError("Invalid Blake2b parameters");
     }
     // constructor called with data argument set
     if (n_args >= 1) {
@@ -80,9 +88,9 @@ STATIC mp_obj_t mod_trezorcrypto_Blake2b_digest(mp_obj_t self) {
     uint8_t out[BLAKE2B_DIGEST_LENGTH];
     BLAKE2B_CTX ctx;
     memcpy(&ctx, &(o->ctx), sizeof(BLAKE2B_CTX));
-    blake2b_Final(&ctx, out, BLAKE2B_DIGEST_LENGTH);
+    blake2b_Final(&ctx, out, ctx.outlen);
     memset(&ctx, 0, sizeof(BLAKE2B_CTX));
-    return mp_obj_new_bytes(out, sizeof(out));
+    return mp_obj_new_bytes(out, o->ctx.outlen);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_trezorcrypto_Blake2b_digest_obj, mod_trezorcrypto_Blake2b_digest);
 
diff --git a/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2s.h b/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2s.h
index 927c31a6a2..79ce0f326d 100644
--- a/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2s.h
+++ b/embed/extmod/modtrezorcrypto/modtrezorcrypto-blake2s.h
@@ -33,21 +33,29 @@ typedef struct _mp_obj_Blake2s_t {
 
 STATIC mp_obj_t mod_trezorcrypto_Blake2s_update(mp_obj_t self, mp_obj_t data);
 
-/// def __init__(self, data: bytes = None, key: bytes = None) -> None:
+/// def __init__(self, data: bytes = None, outlen: int = Blake2s.digest_size, key: bytes = None) -> None:
 ///     '''
 ///     Creates a hash context object.
 ///     '''
 STATIC mp_obj_t mod_trezorcrypto_Blake2s_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
-    mp_arg_check_num(n_args, n_kw, 0, 2, false);
+    mp_arg_check_num(n_args, n_kw, 0, 3, false);
     mp_obj_Blake2s_t *o = m_new_obj(mp_obj_Blake2s_t);
     o->base.type = type;
+    int res = 0;
     // constructor called with key argument set
-    if (n_args == 2) {
+    if (n_args == 3) {
+        size_t outlen = mp_obj_get_int(args[1]);
         mp_buffer_info_t key;
-        mp_get_buffer_raise(args[1], &key, MP_BUFFER_READ);
-        blake2s_InitKey(&(o->ctx), BLAKE2S_DIGEST_LENGTH, key.buf, key.len);
+        mp_get_buffer_raise(args[2], &key, MP_BUFFER_READ);
+        res = blake2s_InitKey(&(o->ctx), outlen, key.buf, key.len);
+    } else if (n_args == 2) {
+        size_t outlen = mp_obj_get_int(args[1]);
+        res = blake2s_Init(&(o->ctx), outlen);
     } else {
-        blake2s_Init(&(o->ctx), BLAKE2S_DIGEST_LENGTH);
+        res = blake2s_Init(&(o->ctx), BLAKE2S_DIGEST_LENGTH);
+    }
+    if (res < 0) {
+        mp_raise_ValueError("Invalid Blake2s parameters");
     }
     // constructor called with data argument set
     if (n_args >= 1) {
@@ -80,9 +88,9 @@ STATIC mp_obj_t mod_trezorcrypto_Blake2s_digest(mp_obj_t self) {
     uint8_t out[BLAKE2S_DIGEST_LENGTH];
     BLAKE2S_CTX ctx;
     memcpy(&ctx, &(o->ctx), sizeof(BLAKE2S_CTX));
-    blake2s_Final(&ctx, out, BLAKE2S_DIGEST_LENGTH);
+    blake2s_Final(&ctx, out, ctx.outlen);
     memset(&ctx, 0, sizeof(BLAKE2S_CTX));
-    return mp_obj_new_bytes(out, sizeof(out));
+    return mp_obj_new_bytes(out, o->ctx.outlen);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_trezorcrypto_Blake2s_digest_obj, mod_trezorcrypto_Blake2s_digest);
 
diff --git a/tests/test_trezor.crypto.hashlib.blake2b.py b/tests/test_trezor.crypto.hashlib.blake2b.py
index 1f66a631b0..20255e7dc1 100644
--- a/tests/test_trezor.crypto.hashlib.blake2b.py
+++ b/tests/test_trezor.crypto.hashlib.blake2b.py
@@ -18,11 +18,11 @@ class TestCryptoBlake2b(unittest.TestCase):
     def test_digest(self):
         key = unhexlify('000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f')
         for d, h in self.vectors:
-            self.assertEqual(hashlib.blake2b(unhexlify(d), key).digest(), unhexlify(h))
+            self.assertEqual(hashlib.blake2b(unhexlify(d), hashlib.blake2b.digest_size, key).digest(), unhexlify(h))
 
     def test_update(self):
         key = unhexlify('000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f')
-        x = hashlib.blake2b(b'', key)
+        x = hashlib.blake2b(b'', hashlib.blake2b.digest_size, key)
         x.update(bytes(range(10)))
         self.assertEqual(x.digest(), unhexlify('4fe181f54ad63a2983feaaf77d1e7235c2beb17fa328b6d9505bda327df19fc37f02c4b6f0368ce23147313a8e5738b5fa2a95b29de1c7f8264eb77b69f585cd'))
         x.update(bytes(range(10, 30)))
diff --git a/tests/test_trezor.crypto.hashlib.blake2s.py b/tests/test_trezor.crypto.hashlib.blake2s.py
index 0d4d229a46..6f389b6f3c 100644
--- a/tests/test_trezor.crypto.hashlib.blake2s.py
+++ b/tests/test_trezor.crypto.hashlib.blake2s.py
@@ -19,11 +19,11 @@ class TestCryptoBlake2s(unittest.TestCase):
     def test_digest(self):
         key = unhexlify('000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f')
         for d, h in self.vectors:
-            self.assertEqual(hashlib.blake2s(unhexlify(d), key).digest(), unhexlify(h))
+            self.assertEqual(hashlib.blake2s(unhexlify(d), hashlib.blake2s.digest_size, key).digest(), unhexlify(h))
 
     def test_update(self):
         key = unhexlify('000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f')
-        x = hashlib.blake2s(b'', key)
+        x = hashlib.blake2s(b'', hashlib.blake2s.digest_size, key)
         x.update(bytes(range(10)))
         self.assertEqual(x.digest(), unhexlify('f5c4b2ba1a00781b13aba0425242c69cb1552f3f71a9a3bb22b4a6b4277b46dd'))
         x.update(bytes(range(10, 30)))