diff --git a/src/utils.c b/src/utils.c
index 0b7d583..9c16b6f 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -54,7 +54,8 @@ int local_strchr(char *string, char ch) {
 }
 
 // Almost like U4BE except that it takes `size` as a parameter.
-uint32_t u32_from_BE(uint8_t *in, uint8_t size) {
+// The `strict` parameter defines whether we should throw in case of a length > 4.
+uint32_t u32_from_BE(uint8_t *in, uint8_t size, bool strict) {
     uint32_t res = 0;
     if (size == 1) {
         res = in[0];
@@ -62,8 +63,11 @@ uint32_t u32_from_BE(uint8_t *in, uint8_t size) {
         res = (in[0] << 8) | in[1];
     } else if (size == 3) {
         res = (in[0] << 16) | (in[1] << 8) | in[2];
-    } else {
+    } else if (size == 4) {
         res = (in[0] << 24) | (in[1] << 16) | (in[2] << 8) | in[3];
+    } else if (strict && size != 0) {
+        PRINTF("Unexpected format\n");
+        THROW(EXCEPTION);
     }
     return res;
 }
diff --git a/src/utils.h b/src/utils.h
index 582fb62..b13c5e2 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -32,7 +32,7 @@ int local_strchr(char* string, char ch);
 void u32_to_str(char* dest, uint8_t dest_size, uint32_t in);
 
 // Converts a list of bytes (in BE) of length `size` to a uint32_t.
-uint32_t u32_from_BE(uint8_t* in, uint8_t size);
+uint32_t u32_from_BE(uint8_t* in, uint8_t size, bool strict);
 
 void amountToString(uint8_t* amount,
                     uint8_t amount_len,
diff --git a/src_features/signTx/logic_signTx.c b/src_features/signTx/logic_signTx.c
index 8be1d51..989331b 100644
--- a/src_features/signTx/logic_signTx.c
+++ b/src_features/signTx/logic_signTx.c
@@ -248,9 +248,9 @@ void finalizeParsing(bool direct) {
         uint32_t id = 0;
 
         if (txContext.txType == LEGACY) {
-            id = u32_from_BE(txContext.content->v, txContext.content->vLength);
+            id = u32_from_BE(txContext.content->v, txContext.content->vLength, true);
         } else if (txContext.txType == EIP2930) {
-            id = u32_from_BE(txContext.content->chainID.value, txContext.content->chainID.length);
+            id = u32_from_BE(txContext.content->chainID.value, txContext.content->chainID.length, false);
         } else {
             PRINTF("TxType `%u` not supported while checking for chainID\n", txContext.txType);
             return;
@@ -388,7 +388,7 @@ void finalizeParsing(bool direct) {
     // Prepare chainID field
     if (genericUI) {
         if (txContext.txType == LEGACY) {
-            uint32_t id = u32_from_BE(txContext.content->v, txContext.content->vLength);
+            uint32_t id = u32_from_BE(txContext.content->v, txContext.content->vLength, true);
             u32_to_str((char *) strings.common.chainID, sizeof(strings.common.chainID), id);
         } else if (txContext.txType == EIP2930) {
             uint256_t chainID;
diff --git a/src_features/signTx/ui_common_signTx.c b/src_features/signTx/ui_common_signTx.c
index 54ce048..ac3023a 100644
--- a/src_features/signTx/ui_common_signTx.c
+++ b/src_features/signTx/ui_common_signTx.c
@@ -8,7 +8,7 @@ unsigned int io_seproxyhal_touch_tx_ok(const bagl_element_t *e) {
     uint8_t signatureLength;
     cx_ecfp_private_key_t privateKey;
     uint32_t tx = 0;
-    uint32_t v = u32_from_BE(tmpContent.txContent.v, tmpContent.txContent.vLength);
+    uint32_t v = u32_from_BE(tmpContent.txContent.v, tmpContent.txContent.vLength, true);
     io_seproxyhal_io_heartbeat();
     os_perso_derive_node_bip32(CX_CURVE_256K1,
                                tmpCtx.transactionContext.bip32Path,
diff --git a/src_features/signTx/ui_flow_signTx.c b/src_features/signTx/ui_flow_signTx.c
index 3edf610..345fef8 100644
--- a/src_features/signTx/ui_flow_signTx.c
+++ b/src_features/signTx/ui_flow_signTx.c
@@ -173,9 +173,9 @@ void ux_approve_tx(bool dataPresent) {
 
     uint32_t id;
     if (txContext.txType == LEGACY) {
-        id = u32_from_BE(txContext.content->v, txContext.content->vLength);
+        id = u32_from_BE(txContext.content->v, txContext.content->vLength, true);
     } else if (txContext.txType == EIP2930) {
-        id = u32_from_BE(txContext.content->chainID.value, txContext.content->chainID.length);
+        id = u32_from_BE(txContext.content->chainID.value, txContext.content->chainID.length, false);
     } else {
         PRINTF("TxType `%u` not supported while preparing to approve tx\n", txContext.txType);
         THROW(0x6501);