diff --git a/src/engine.rs b/src/engine.rs
index a713defdf..fa2f2e7b3 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -14,7 +14,7 @@ use crate::parameters::{
 };
 
 use crate::precompiles::Precompiles;
-use crate::prelude::{Address, TryInto, Vec, H256, U256};
+use crate::prelude::{is_valid_account_id, Address, TryInto, Vec, H256, U256};
 use crate::sdk;
 use crate::state::AuroraStackState;
 use crate::storage::{address_to_key, bytes_to_key, storage_to_key, KeyPrefix, KeyPrefixU8};
@@ -128,6 +128,50 @@ impl ExitIntoResult for ExitReason {
     }
 }
 
+pub const ERR_INVALID_NEP141_ACCOUNT_ID: &str = "ERR_INVALID_NEP141_ACCOUNT_ID";
+
+#[derive(Debug)]
+pub enum GetErc20FromNep141Error {
+    InvalidNep141AccountId,
+    Nep141NotFound,
+}
+
+impl GetErc20FromNep141Error {
+    pub fn to_str(&self) -> &str {
+        match self {
+            Self::InvalidNep141AccountId => ERR_INVALID_NEP141_ACCOUNT_ID,
+            Self::Nep141NotFound => "ERR_NEP141_NOT_FOUND",
+        }
+    }
+}
+
+impl AsRef<[u8]> for GetErc20FromNep141Error {
+    fn as_ref(&self) -> &[u8] {
+        self.to_str().as_bytes()
+    }
+}
+
+#[derive(Debug)]
+pub enum RegisterTokenError {
+    InvalidNep141AccountId,
+    TokenAlreadyRegistered,
+}
+
+impl RegisterTokenError {
+    pub fn to_str(&self) -> &str {
+        match self {
+            Self::InvalidNep141AccountId => ERR_INVALID_NEP141_ACCOUNT_ID,
+            Self::TokenAlreadyRegistered => "ERR_NEP141_TOKEN_ALREADY_REGISTERED",
+        }
+    }
+}
+
+impl AsRef<[u8]> for RegisterTokenError {
+    fn as_ref(&self) -> &[u8] {
+        self.to_str().as_bytes()
+    }
+}
+
 #[derive(Debug)]
 pub enum EngineStateError {
     NotFound,
@@ -465,15 +509,33 @@ impl Engine {
             .map(|result| Address(result.as_slice().try_into().unwrap()))
     }
 
-    pub fn register_token(&mut self, erc20_token: &[u8], nep141_token: &[u8]) {
-        // Check that this nep141 token was not registered before, they can only be registered once.
-        let map = Self::nep141_erc20_map();
-        assert!(map.lookup_left(nep141_token).is_none());
-        map.insert(nep141_token, erc20_token);
+    pub fn register_token(
+        &mut self,
+        erc20_token: &[u8],
+        nep141_token: &[u8],
+    ) -> Result<(), RegisterTokenError> {
+        match Self::get_erc20_from_nep141(nep141_token) {
+            Err(GetErc20FromNep141Error::Nep141NotFound) => (),
+            Err(GetErc20FromNep141Error::InvalidNep141AccountId) => {
+                return Err(RegisterTokenError::InvalidNep141AccountId)
+            }
+            Ok(_) => return Err(RegisterTokenError::TokenAlreadyRegistered),
+        }
+
+        Self::nep141_erc20_map().insert(nep141_token, erc20_token);
+        Ok(())
     }
 
-    pub fn get_erc20_from_nep141(&self, nep141_token: &[u8]) -> Option<Vec<u8>> {
-        Self::nep141_erc20_map().lookup_left(nep141_token)
+    pub fn get_erc20_from_nep141(
+        nep141_account_id: &[u8],
+    ) -> Result<Vec<u8>, GetErc20FromNep141Error> {
+        if !is_valid_account_id(nep141_account_id) {
+            return Err(GetErc20FromNep141Error::InvalidNep141AccountId);
+        }
+
+        Self::nep141_erc20_map()
+            .lookup_left(nep141_account_id)
+            .ok_or(GetErc20FromNep141Error::Nep141NotFound)
     }
 
     /// Transfers an amount from a given sender to a receiver, provided that
@@ -505,8 +567,6 @@ impl Engine {
         let str_amount = crate::prelude::format!("\"{}\"", args.amount);
         let output_on_fail = str_amount.as_bytes();
 
-        let token = sdk::predecessor_account_id();
-
         // Parse message to determine recipient and fee
         let (recipient, fee) = {
             // Message format:
@@ -533,13 +593,11 @@ impl Engine {
             (recipient, fee)
         };
 
+        let token = sdk::predecessor_account_id();
         let erc20_token = Address(unwrap_res_or_finish!(
-            unwrap_res_or_finish!(
-                self.get_erc20_from_nep141(token.as_slice()).ok_or(()),
-                output_on_fail
-            )
-            .as_slice()
-            .try_into(),
+            unwrap_res_or_finish!(Self::get_erc20_from_nep141(&token), output_on_fail)
+                .as_slice()
+                .try_into(),
             output_on_fail
         ));
 
diff --git a/src/lib.rs b/src/lib.rs
index df76445ad..3f2843730 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -81,9 +81,9 @@ mod contract {
     #[cfg(feature = "evm_bully")]
     use crate::parameters::{BeginBlockArgs, BeginChainArgs};
     use crate::parameters::{
-        DeployErc20TokenArgs, ExpectUtf8, FunctionCallArgs, GetStorageAtArgs, InitCallArgs,
-        IsUsedProofCallArgs, NEP141FtOnTransferArgs, NewCallArgs, PauseEthConnectorCallArgs,
-        SetContractDataCallArgs, TransferCallCallArgs, ViewCallArgs,
+        DeployErc20TokenArgs, ExpectUtf8, FunctionCallArgs, GetErc20FromNep141CallArgs,
+        GetStorageAtArgs, InitCallArgs, IsUsedProofCallArgs, NEP141FtOnTransferArgs, NewCallArgs,
+        PauseEthConnectorCallArgs, SetContractDataCallArgs, TransferCallCallArgs, ViewCallArgs,
     };
 
     use crate::json::parse_json;
@@ -362,7 +362,12 @@ mod contract {
         )
         .map(|res| {
             let address = H160(res.result.as_slice().try_into().unwrap());
-            engine.register_token(address.as_bytes(), args.nep141.as_bytes());
+            crate::log!(
+                crate::prelude::format!("Deployed ERC-20 in Aurora at: {:#?}", address).as_str()
+            );
+            engine
+                .register_token(address.as_bytes(), &args.nep141.as_bytes())
+                .sdk_unwrap();
             res.result.try_to_vec().sdk_expect("ERR_SERIALIZE")
         })
         .sdk_process();
@@ -573,10 +578,13 @@ mod contract {
 
     #[no_mangle]
     pub extern "C" fn get_erc20_from_nep141() {
+        let args: GetErc20FromNep141CallArgs =
+            GetErc20FromNep141CallArgs::try_from_slice(&sdk::read_input())
+                .sdk_expect("ERR_ARG_PARSE");
+
         sdk::return_output(
-            Engine::nep141_erc20_map()
-                .lookup_left(sdk::read_input().as_slice())
-                .sdk_expect("NEP141_NOT_FOUND")
+            Engine::get_erc20_from_nep141(&args.nep141.as_bytes())
+                .sdk_unwrap()
                 .as_slice(),
         );
     }
diff --git a/src/parameters.rs b/src/parameters.rs
index c2b62bfa2..58cd1c730 100644
--- a/src/parameters.rs
+++ b/src/parameters.rs
@@ -87,11 +87,15 @@ pub struct ViewCallArgs {
     pub input: Vec<u8>,
 }
 
+/// Borsh-encoded parameters for `deploy_erc20_token` function.
 #[derive(BorshSerialize, BorshDeserialize, Debug, Eq, PartialEq)]
 pub struct DeployErc20TokenArgs {
     pub nep141: AccountId,
 }
 
+/// Borsh-encoded parameters for `get_erc20_from_nep141` function.
+pub type GetErc20FromNep141CallArgs = DeployErc20TokenArgs;
+
 /// Borsh-encoded parameters for the `get_storage_at` function.
 #[derive(BorshSerialize, BorshDeserialize)]
 pub struct GetStorageAtArgs {