diff --git a/core/src/apps/eos/actions/__init__.py b/core/src/apps/eos/actions/__init__.py
index 5400448c0..c47b827f4 100644
--- a/core/src/apps/eos/actions/__init__.py
+++ b/core/src/apps/eos/actions/__init__.py
@@ -67,8 +67,7 @@ async def process_action(
         await process_unknown_action(ctx, w, action)
 
     writers.write_action_common(sha, action.common)
-    writers.write_variant32(sha, len(w))
-    writers.write_bytes_unchecked(sha, w)
+    writers.write_bytes_prefixed(sha, w)
 
 
 async def process_unknown_action(
diff --git a/core/src/apps/eos/sign_tx.py b/core/src/apps/eos/sign_tx.py
index d437e4c95..514e99a8f 100644
--- a/core/src/apps/eos/sign_tx.py
+++ b/core/src/apps/eos/sign_tx.py
@@ -32,7 +32,7 @@ async def sign_tx(ctx: wire.Context, msg: EosSignTx, keychain: Keychain) -> EosS
     await _init(ctx, sha, msg)
     await _actions(ctx, sha, msg.num_actions)
     writers.write_variant32(sha, 0)
-    writers.write_bytes_unchecked(sha, bytearray(32))
+    writers.write_bytes_fixed(sha, bytearray(32), 32)
 
     digest = sha.get_digest()
     signature = secp256k1.sign(
@@ -43,7 +43,7 @@ async def sign_tx(ctx: wire.Context, msg: EosSignTx, keychain: Keychain) -> EosS
 
 
 async def _init(ctx: wire.Context, sha: HashWriter, msg: EosSignTx) -> None:
-    writers.write_bytes_unchecked(sha, msg.chain_id)
+    writers.write_bytes_fixed(sha, msg.chain_id, 32)
     writers.write_header(sha, msg.header)
     writers.write_variant32(sha, 0)
     writers.write_variant32(sha, msg.num_actions)
diff --git a/core/src/apps/eos/writers.py b/core/src/apps/eos/writers.py
index fc6cf589a..aca117d7c 100644
--- a/core/src/apps/eos/writers.py
+++ b/core/src/apps/eos/writers.py
@@ -1,4 +1,7 @@
+from protobuf import dump_uvarint
+
 from apps.common.writers import (
+    write_bytes_fixed,
     write_bytes_unchecked,
     write_uint8,
     write_uint16_le,
@@ -31,7 +34,7 @@ def write_auth(w: Writer, auth: EosAuthorization) -> None:
     write_variant32(w, len(auth.keys))
     for key in auth.keys:
         write_variant32(w, key.type)
-        write_bytes_unchecked(w, key.key)
+        write_bytes_fixed(w, key.key, 33)
         write_uint16_le(w, key.weight)
 
     write_variant32(w, len(auth.accounts))
@@ -59,8 +62,7 @@ def write_action_transfer(w: Writer, msg: EosActionTransfer) -> None:
     write_uint64_le(w, msg.sender)
     write_uint64_le(w, msg.receiver)
     write_asset(w, msg.quantity)
-    write_variant32(w, len(msg.memo))
-    write_bytes_unchecked(w, msg.memo)
+    write_bytes_prefixed(w, msg.memo)
 
 
 def write_action_buyram(w: Writer, msg: EosActionBuyRam) -> None:
@@ -154,12 +156,9 @@ def write_asset(w: Writer, asset: EosAsset) -> None:
 
 
 def write_variant32(w: Writer, value: int) -> None:
-    variant = bytearray()
-    while True:
-        b = value & 0x7F
-        value >>= 7
-        b |= (value > 0) << 7
-        variant.append(b)
-        if value == 0:
-            break
-    write_bytes_unchecked(w, bytes(variant))
+    dump_uvarint(w.extend, value)
+
+
+def write_bytes_prefixed(w: Writer, data: bytes) -> None:
+    write_variant32(w, len(data))
+    write_bytes_unchecked(w, data)