diff --git a/common/protob/messages-ethereum.proto b/common/protob/messages-ethereum.proto
index 2f6ff12e565..21dd426d0c8 100644
--- a/common/protob/messages-ethereum.proto
+++ b/common/protob/messages-ethereum.proto
@@ -65,7 +65,7 @@ message EthereumSignTx {
     optional bytes value = 6;               // <=256 bit unsigned big endian (in wei)
     optional bytes data_initial_chunk = 7;  // The initial data chunk (<= 1024 bytes)
     optional uint32 data_length = 8;        // Length of transaction payload
-    optional uint32 chain_id = 9;           // Chain Id for EIP 155
+    optional uint64 chain_id = 9;           // Chain Id for EIP 155
     optional uint32 tx_type = 10;           // Used for Wanchain
 }
 
@@ -86,7 +86,7 @@ message EthereumSignTxEIP1559 {
     required bytes value = 7;               // <=256 bit unsigned big endian (in wei)
     optional bytes data_initial_chunk = 8 [default=''];  // The initial data chunk (<= 1024 bytes)
     required uint32 data_length = 9;        // Length of transaction payload
-    required uint32 chain_id = 10;           // Chain Id for EIP 155
+    required uint64 chain_id = 10;           // Chain Id for EIP 155
     repeated EthereumAccessList access_list = 11; // Access List
 
     message EthereumAccessList {
@@ -104,7 +104,7 @@ message EthereumSignTxEIP1559 {
  */
 message EthereumTxRequest {
     optional uint32 data_length = 1;    // Number of bytes being requested (<= 1024)
-    optional uint32 signature_v = 2;    // Computed signature (recovery parameter, limited to 27 or 28)
+    optional uint64 signature_v = 2;    // Computed signature (recovery parameter, limited to 27 or 28)
     optional bytes signature_r = 3;     // Computed signature R component (256 bit)
     optional bytes signature_s = 4;     // Computed signature S component (256 bit)
 }
diff --git a/core/.changelog.d/1771.added b/core/.changelog.d/1771.added
new file mode 100644
index 00000000000..fe5e9ab41aa
--- /dev/null
+++ b/core/.changelog.d/1771.added
@@ -0,0 +1 @@
+Ethereum: support 64-bit chain IDs
diff --git a/crypto/address.c b/crypto/address.c
index 8f3aa9734ab..6379489b097 100644
--- a/crypto/address.c
+++ b/crypto/address.c
@@ -58,7 +58,7 @@ bool address_check_prefix(const uint8_t *addr, uint32_t address_type) {
 #include "sha3.h"
 
 void ethereum_address_checksum(const uint8_t *addr, char *address, bool rskip60,
-                               uint32_t chain_id) {
+                               uint64_t chain_id) {
   const char *hex = "0123456789abcdef";
   for (int i = 0; i < 20; i++) {
     address[i * 2] = hex[(addr[i] >> 4) & 0xF];
diff --git a/crypto/address.h b/crypto/address.h
index 8147f2c35a8..e799484ee9a 100644
--- a/crypto/address.h
+++ b/crypto/address.h
@@ -34,7 +34,7 @@ void address_write_prefix_bytes(uint32_t address_type, uint8_t *out);
 bool address_check_prefix(const uint8_t *addr, uint32_t address_type);
 #if USE_ETHEREUM
 void ethereum_address_checksum(const uint8_t *addr, char *address, bool rskip60,
-                               uint32_t chain_id);
+                               uint64_t chain_id);
 #endif
 
 #endif
diff --git a/legacy/firmware/.changelog.d/1771.added b/legacy/firmware/.changelog.d/1771.added
new file mode 100644
index 00000000000..fe5e9ab41aa
--- /dev/null
+++ b/legacy/firmware/.changelog.d/1771.added
@@ -0,0 +1 @@
+Ethereum: support 64-bit chain IDs
diff --git a/legacy/firmware/ethereum.c b/legacy/firmware/ethereum.c
index edb51f299db..7da5a188193 100644
--- a/legacy/firmware/ethereum.c
+++ b/legacy/firmware/ethereum.c
@@ -37,14 +37,16 @@
 #include "transaction.h"
 #include "util.h"
 
-/* maximum supported chain id.  v must fit in an uint32_t. */
-#define MAX_CHAIN_ID 2147483629
+/* maximum supported chain id.
+ * signature_v must also fit in an uint64_t.
+ */
+#define MAX_CHAIN_ID ((0xFFFFFFFFFFFFFFFF - 35) >> 1)
 
 static bool ethereum_signing = false;
 static uint32_t data_total, data_left;
 static EthereumTxRequest msg_tx_request;
 static CONFIDENTIAL uint8_t privkey[32];
-static uint32_t chain_id;
+static uint64_t chain_id;
 static uint32_t tx_type;
 struct SHA3_CTX keccak_ctx = {0};
 
@@ -118,20 +120,24 @@ static void hash_rlp_field(const uint8_t *buf, size_t size) {
  * Push an RLP encoded number to the hash buffer.
  * Ethereum yellow paper says to convert to big endian and strip leading zeros.
  */
-static void hash_rlp_number(uint32_t number) {
+static void hash_rlp_number(uint64_t number) {
   if (!number) {
     return;
   }
-  uint8_t data[4] = {0};
-  data[0] = (number >> 24) & 0xff;
-  data[1] = (number >> 16) & 0xff;
-  data[2] = (number >> 8) & 0xff;
-  data[3] = (number)&0xff;
+  uint8_t data[8] = {0};
+  data[0] = (number >> 56) & 0xff;
+  data[1] = (number >> 48) & 0xff;
+  data[2] = (number >> 40) & 0xff;
+  data[3] = (number >> 32) & 0xff;
+  data[4] = (number >> 24) & 0xff;
+  data[5] = (number >> 16) & 0xff;
+  data[6] = (number >> 8) & 0xff;
+  data[7] = (number)&0xff;
   int offset = 0;
   while (!data[offset]) {
     offset++;
   }
-  hash_rlp_field(data + offset, 4 - offset);
+  hash_rlp_field(data + offset, 8 - offset);
 }
 
 /*
@@ -153,18 +159,18 @@ static int rlp_calculate_length(int length, uint8_t firstbyte) {
   }
 }
 
-static int rlp_calculate_number_length(uint32_t number) {
-  if (number <= 0x7f) {
-    return 1;
-  } else if (number <= 0xff) {
-    return 2;
-  } else if (number <= 0xffff) {
-    return 3;
-  } else if (number <= 0xffffff) {
-    return 4;
-  } else {
-    return 5;
+/* If number is less than 0x80 the RLP encoding is iteself (1 byte).
+ * If it is 0x80 or larger, RLP encoding is 1 + length in bytes.
+ */
+static int rlp_calculate_number_length(uint64_t number) {
+  int length = 1;
+  if (number >= 0x80) {
+    while (number) {
+      length++;
+      number = number >> 8;
+    }
   }
+  return length;
 }
 
 static void send_request_chunk(void) {
diff --git a/legacy/firmware/ethereum_tokens.c.mako b/legacy/firmware/ethereum_tokens.c.mako
index a16d60da934..19737f84db8 100644
--- a/legacy/firmware/ethereum_tokens.c.mako
+++ b/legacy/firmware/ethereum_tokens.c.mako
@@ -13,7 +13,7 @@ const TokenType tokens[TOKENS_COUNT] = {
 static const TokenType _UnknownToken = { 0, "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff", " UNKN", 0 };
 const TokenType *UnknownToken = &_UnknownToken;
 
-const TokenType *tokenByChainAddress(uint32_t chain_id, const uint8_t *address)
+const TokenType *tokenByChainAddress(uint64_t chain_id, const uint8_t *address)
 {
 	if (!address) return 0;
 	for (int i = 0; i < TOKENS_COUNT; i++) {
diff --git a/legacy/firmware/ethereum_tokens.h.mako b/legacy/firmware/ethereum_tokens.h.mako
index 12008d7efdb..160506c3d33 100644
--- a/legacy/firmware/ethereum_tokens.h.mako
+++ b/legacy/firmware/ethereum_tokens.h.mako
@@ -10,7 +10,7 @@
 #define TOKENS_COUNT ${len(erc20_list)}
 
 typedef struct {
-	uint32_t chain_id;
+	uint64_t chain_id;
 	const char * const address;
 	const char * const ticker;
 	int decimals;
@@ -20,6 +20,6 @@ extern const TokenType tokens[TOKENS_COUNT];
 
 extern const TokenType *UnknownToken;
 
-const TokenType *tokenByChainAddress(uint32_t chain_id, const uint8_t *address);
+const TokenType *tokenByChainAddress(uint64_t chain_id, const uint8_t *address);
 
 #endif
diff --git a/legacy/firmware/fsm_msg_ethereum.h b/legacy/firmware/fsm_msg_ethereum.h
index 20115bb6847..82d4fa4d503 100644
--- a/legacy/firmware/fsm_msg_ethereum.h
+++ b/legacy/firmware/fsm_msg_ethereum.h
@@ -99,7 +99,7 @@ void fsm_msgEthereumGetAddress(const EthereumGetAddress *msg) {
   uint32_t slip44 =
       (msg->address_n_count > 1) ? (msg->address_n[1] & 0x7fffffff) : 0;
   bool rskip60 = false;
-  uint32_t chain_id = 0;
+  uint64_t chain_id = 0;
   // constants from trezor-common/defs/ethereum/networks.json
   switch (slip44) {
     case 137:
diff --git a/python/.changelog.d/1771.added b/python/.changelog.d/1771.added
new file mode 100644
index 00000000000..fe5e9ab41aa
--- /dev/null
+++ b/python/.changelog.d/1771.added
@@ -0,0 +1 @@
+Ethereum: support 64-bit chain IDs
diff --git a/python/src/trezorlib/messages.py b/python/src/trezorlib/messages.py
index 4acc24239d5..dd0b5bccabc 100644
--- a/python/src/trezorlib/messages.py
+++ b/python/src/trezorlib/messages.py
@@ -3942,7 +3942,7 @@ class EthereumSignTx(protobuf.MessageType):
         6: protobuf.Field("value", "bytes", repeated=False, required=False),
         7: protobuf.Field("data_initial_chunk", "bytes", repeated=False, required=False),
         8: protobuf.Field("data_length", "uint32", repeated=False, required=False),
-        9: protobuf.Field("chain_id", "uint32", repeated=False, required=False),
+        9: protobuf.Field("chain_id", "uint64", repeated=False, required=False),
         10: protobuf.Field("tx_type", "uint32", repeated=False, required=False),
     }
 
@@ -3984,7 +3984,7 @@ class EthereumSignTxEIP1559(protobuf.MessageType):
         7: protobuf.Field("value", "bytes", repeated=False, required=True),
         8: protobuf.Field("data_initial_chunk", "bytes", repeated=False, required=False),
         9: protobuf.Field("data_length", "uint32", repeated=False, required=True),
-        10: protobuf.Field("chain_id", "uint32", repeated=False, required=True),
+        10: protobuf.Field("chain_id", "uint64", repeated=False, required=True),
         11: protobuf.Field("access_list", "EthereumAccessList", repeated=True, required=False),
     }
 
@@ -4020,7 +4020,7 @@ class EthereumTxRequest(protobuf.MessageType):
     MESSAGE_WIRE_TYPE = 59
     FIELDS = {
         1: protobuf.Field("data_length", "uint32", repeated=False, required=False),
-        2: protobuf.Field("signature_v", "uint32", repeated=False, required=False),
+        2: protobuf.Field("signature_v", "uint64", repeated=False, required=False),
         3: protobuf.Field("signature_r", "bytes", repeated=False, required=False),
         4: protobuf.Field("signature_s", "bytes", repeated=False, required=False),
     }
diff --git a/tests/device_tests/test_msg_ethereum_signtx_eip155.py b/tests/device_tests/test_msg_ethereum_signtx_eip155.py
index 43260dd5539..0dfcfc931d7 100644
--- a/tests/device_tests/test_msg_ethereum_signtx_eip155.py
+++ b/tests/device_tests/test_msg_ethereum_signtx_eip155.py
@@ -20,6 +20,8 @@
 from trezorlib import ethereum
 from trezorlib.tools import parse_path
 
+MAX_CHAIN_ID = 2147483629
+
 VECTORS_CHAIN_IDS = (  # chain_id, slip44, sig_v, sig_r, sig_s
     # Ethereum
     (
@@ -101,6 +103,66 @@
             "1447ba45be9fca42bcbf250389403245c8c1b0476e60b96dea320b0a596b5528",
         ),
     ),
+    # Previous max chain id
+    (
+        2147483639,
+        1,
+        (
+            4294967314,
+            "f06ba56a3d3602a3d39a614375b2867f8a867354ba17fde98a5cb5f1806320d1",
+            "7bc197e0f656e52183805abada49c7d41f5d2b929f1ae0ebe99618286dfed116",
+        ),
+    ),
+    # PALM
+    (
+        11297108109,
+        60,
+        (
+            22594216254,
+            "9d05ca7cdcf971f3114c0ef8d636c5aae1353bb227e04ec1198c60d874e676c0",
+            "35414067209e27fb690d9387264c74e334e25a117705f3583fb24434a952c9ca",
+        ),
+    ),
+    # PALM
+    (
+        11297108109,
+        1,
+        (
+            22594216253,
+            "cccccef8f6636f316e69a1239436f9d61021501ba20ed72b6528c84b2f727980",
+            "614cb533a5d73cbf92ba4683c87c9238d0547572ee8f0f821ab1decdfc9639b8",
+        ),
+    ),
+    # MAX_CHAIN_ID
+    (
+        MAX_CHAIN_ID,
+        1,
+        (
+            4294967293,
+            "97f217d851c9f54013d7792d3b06492abbeda334191687323f08e03e979bd6c9",
+            "6a5f60d9abb1fa76be8ab76d3c879e1f0187e432692e3e9adce60642f06abe74",
+        ),
+    ),
+    # MAX_CHAIN_ID+1
+    (
+        MAX_CHAIN_ID + 1,
+        1,
+        (
+            4294967296,
+            "f643499025c61025d27f7815ed1b1dcd92233548ebdd13bdd056e9cf3f84a853",
+            "33f363b014e5a404bec8479bb08649a6843f65c1f3166d3289211fb5361dab45",
+        ),
+    ),
+    # Max uint64
+    (
+        0xFFFF_FFFF_FFFF_FFFF,
+        1,
+        (
+            36893488147419103266,
+            "7bf581e8c7ff7d0e94d25eaa476de928d444b180fe50a91374b8883ff5dee3a8",
+            "3a3efa7a3f97043a999b3183d958a03126ec2652608c376c4626850b9b6a33fa",
+        ),
+    ),
 )