diff --git a/core/src/apps/bitcoin/sign_tx/__init__.py b/core/src/apps/bitcoin/sign_tx/__init__.py
index 7400e2085e..39b880f878 100644
--- a/core/src/apps/bitcoin/sign_tx/__init__.py
+++ b/core/src/apps/bitcoin/sign_tx/__init__.py
@@ -1,5 +1,14 @@
+import gc
+
 from trezor import utils, wire
 from trezor.messages.RequestType import TXFINISHED
+from trezor.messages.SignTx import SignTx
+from trezor.messages.TxAckInput import TxAckInput
+from trezor.messages.TxAckOutput import TxAckOutput
+from trezor.messages.TxAckPrevExtraData import TxAckPrevExtraData
+from trezor.messages.TxAckPrevInput import TxAckPrevInput
+from trezor.messages.TxAckPrevMeta import TxAckPrevMeta
+from trezor.messages.TxAckPrevOutput import TxAckPrevOutput
 from trezor.messages.TxRequest import TxRequest
 
 from ..common import BITCOIN_NAMES
@@ -14,14 +23,6 @@ if False:
 
     from protobuf import FieldCache
 
-    from trezor.messages.SignTx import SignTx
-    from trezor.messages.TxAckInput import TxAckInput
-    from trezor.messages.TxAckOutput import TxAckOutput
-    from trezor.messages.TxAckPrevMeta import TxAckPrevMeta
-    from trezor.messages.TxAckPrevInput import TxAckPrevInput
-    from trezor.messages.TxAckPrevOutput import TxAckPrevOutput
-    from trezor.messages.TxAckPrevExtraData import TxAckPrevExtraData
-
     from apps.common.coininfo import CoinInfo
     from apps.common.keychain import Keychain
 
@@ -75,7 +76,18 @@ async def sign_tx(
     signer = signer_class(msg, keychain, coin, approver).signer()
 
     res: TxAckType | bool | None = None
+
+    gc.collect()
     field_cache: FieldCache = {}
+    TxRequest.cache_subordinate_types(field_cache)
+    SignTx.cache_subordinate_types(field_cache)
+    TxAckInput.cache_subordinate_types(field_cache)
+    TxAckOutput.cache_subordinate_types(field_cache)
+    TxAckPrevExtraData.cache_subordinate_types(field_cache)
+    TxAckPrevInput.cache_subordinate_types(field_cache)
+    TxAckPrevMeta.cache_subordinate_types(field_cache)
+    TxAckPrevOutput.cache_subordinate_types(field_cache)
+
     while True:
         req = signer.send(res)
         if isinstance(req, tuple):
diff --git a/core/src/protobuf.py b/core/src/protobuf.py
index c8e3919a1f..5e879b3297 100644
--- a/core/src/protobuf.py
+++ b/core/src/protobuf.py
@@ -148,6 +148,24 @@ class UnicodeType:
     WIRE_TYPE = 2
 
 
+if False:
+    MessageTypeDef = Union[
+        type[UVarintType],
+        type[SVarintType],
+        type[BoolType],
+        EnumType,
+        type[BytesType],
+        type[UnicodeType],
+        type["MessageType"],
+    ]
+    FieldDef = tuple[str, MessageTypeDef, Any]
+    FieldDict = dict[int, FieldDef]
+
+    FieldCache = dict[type["MessageType"], FieldDict]
+
+    LoadedMessageType = TypeVar("LoadedMessageType", bound="MessageType")
+
+
 class MessageType:
     WIRE_TYPE = 2
     UNSTABLE = False
@@ -157,9 +175,21 @@ class MessageType:
     MESSAGE_WIRE_TYPE = -1
 
     @classmethod
-    def get_fields(cls) -> "FieldDict":
+    def get_fields(cls) -> FieldDict:
         return {}
 
+    @classmethod
+    def cache_subordinate_types(cls, field_cache: FieldCache) -> None:
+        if cls in field_cache:
+            fields = field_cache[cls]
+        else:
+            fields = cls.get_fields()
+            field_cache[cls] = fields
+
+        for _, field_type, _ in fields.values():
+            if isinstance(field_type, MessageType):
+                field_type.cache_subordinate_types(field_cache)
+
     def __eq__(self, rhs: Any) -> bool:
         return self.__class__ is rhs.__class__ and self.__dict__ == rhs.__dict__
 
@@ -185,23 +215,6 @@ FLAG_REPEATED = object()
 FLAG_REQUIRED = object()
 FLAG_EXPERIMENTAL = object()
 
-if False:
-    MessageTypeDef = Union[
-        type[UVarintType],
-        type[SVarintType],
-        type[BoolType],
-        EnumType,
-        type[BytesType],
-        type[UnicodeType],
-        type[MessageType],
-    ]
-    FieldDef = tuple[str, MessageTypeDef, Any]
-    FieldDict = dict[int, FieldDef]
-
-    FieldCache = dict[type[MessageType], FieldDict]
-
-    LoadedMessageType = TypeVar("LoadedMessageType", bound=MessageType)
-
 
 def load_message(
     reader: Reader,