diff --git a/package-lock.json b/package-lock.json
index b1df681..3edca2a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@iden3/js-iden3-core",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@iden3/js-iden3-core",
-      "version": "1.2.0",
+      "version": "1.2.1",
       "license": "AGPL-3.0",
       "devDependencies": {
         "@iden3/eslint-config": "https://github.com/iden3/eslint-config",
diff --git a/package.json b/package.json
index d58eefb..b4d9ff3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@iden3/js-iden3-core",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "Low level API to create and manipulate iden3 Claims.",
   "source": "./src/index.ts",
   "typings": "dist/types/index.d.ts",
diff --git a/src/registration.ts b/src/registration.ts
index 0c06f1f..71e488c 100644
--- a/src/registration.ts
+++ b/src/registration.ts
@@ -17,10 +17,11 @@ export const registerNetwork = (network: string): void => {
 };
 
 export const registerDidMethod = (method: string, byte: number): void => {
-  const existingByte = DidMethodByte[method];
-  if (typeof DidMethodByte[method] === 'number' && existingByte !== byte) {
+  if (Object.values(DidMethodByte).includes(byte) && DidMethodByte[method] !== byte) {
     throw new Error(
-      `DID method '${method}' already registered with byte '${existingByte.toString(2)}'`
+      `can't register method '${method}' because DID method byte '${byte.toString(
+        2
+      )}' already registered`
     );
   }
   const max = DidMethodByte[DidMethod.Other];
@@ -47,8 +48,10 @@ export const registerDidMethod = (method: string, byte: number): void => {
  */
 export const registerChainId = (blockchain: string, network: string, chainId: number): void => {
   const key = `${blockchain}:${network}`;
+  const isNotSameValue = typeof ChainIds[key] === 'number' && ChainIds[key] !== chainId;
+  const isValueAlreadyExists = Object.values(ChainIds).includes(chainId);
 
-  if (typeof ChainIds[key] === 'number' && ChainIds[key] !== chainId) {
+  if (isValueAlreadyExists && isNotSameValue) {
     throw new Error(
       `chainId '${blockchain}:${network}' already registered with value '${ChainIds[key]}'`
     );
@@ -145,6 +148,7 @@ export const registerDidMethodNetwork = ({
   }
 
   const key = `${blockchain}:${network}`;
+
   const existedFlag = DidMethodNetwork[method][key];
   if (typeof existedFlag === 'number' && existedFlag !== networkFlag) {
     throw new Error(
@@ -153,5 +157,9 @@ export const registerDidMethodNetwork = ({
       )}'`
     );
   }
+
+  if (Object.values(DidMethodNetwork[method]).includes(networkFlag)) {
+    throw new Error(`DID network flag  ${DidMethodNetwork[method][key]} is already registered`);
+  }
   DidMethodNetwork[method][key] = networkFlag;
 };
diff --git a/tests/did.test.ts b/tests/did.test.ts
index c96e492..580dd45 100644
--- a/tests/did.test.ts
+++ b/tests/did.test.ts
@@ -288,7 +288,7 @@ describe('DID tests', () => {
           network: 'network',
           networkFlag: 0b0001_0001,
           chainId: 102,
-          methodByte: 0b00000100
+          methodByte: 0b00000101
         }
       },
       {
@@ -328,7 +328,7 @@ describe('DID tests', () => {
           blockchain: Blockchain.Polygon,
           network: NetworkId.Mumbai,
           networkFlag: 0b0001_0001,
-          methodByte: 0b0000001
+          methodByte: 0b0000111
         }
       }
     ];
@@ -340,15 +340,15 @@ describe('DID tests', () => {
 
     const d = helperBuildDIDFromType('method', 'chain', 'network');
     // const did = helperBuildDIDFromType('method', 'chain', 'network');
-    expect('4bb86obLkMrifHixMY62WM4iQQVr7u29cxWjMAinrT').toEqual(d.string().split(':').pop());
+    expect('5UtG9EXvF25j3X5uycwr4uy7Hjhni8bMposv3Lgv8o').toEqual(d.string().split(':').pop());
 
     // did
-    const didStr = 'did:method:chain:network:4bb86obLkMrifHixMY62WM4iQQVr7u29cxWjMAinrT';
+    const didStr = 'did:method:chain:network:5UtG9EXvF25j3X5uycwr4uy7Hjhni8bMposv3Lgv8o';
 
     const did3 = DID.parse(didStr);
     const id = DID.idFromDID(did3);
 
-    expect('4bb86obLkMrifHixMY62WM4iQQVr7u29cxWjMAinrT').toEqual(id.string());
+    expect('5UtG9EXvF25j3X5uycwr4uy7Hjhni8bMposv3Lgv8o').toEqual(id.string());
     const method = DID.methodFromId(id);
     expect(DidMethod.method).toBe(method);
     const blockchain = DID.blockchainFromId(id);
@@ -379,7 +379,7 @@ describe('DID tests', () => {
         chainId: 1,
         methodByte: 0b00000010
       },
-      err: "DID method 'iden3' already registered with byte '1'"
+      err: "can't register method 'iden3' because DID method byte '10' already registered"
     },
     {
       description: 'try to write max did method byte',
@@ -389,9 +389,9 @@ describe('DID tests', () => {
         network: NetworkId.Main,
         networkFlag: 0b00100000 | 0b00000001,
         chainId: 1,
-        methodByte: 0b11111111
+        methodByte: 0b111111111
       },
-      err: "Can't register DID method byte: current '11111111', maximum byte allowed: '11111110'"
+      err: "Can't register DID method byte: current '111111111', maximum byte allowed: '11111110'"
     },
     {
       description: 'try to rewrite existing DID Method Network Flag',
@@ -402,6 +402,41 @@ describe('DID tests', () => {
         networkFlag: 0b00100000 | 0b00000011
       },
       err: "DID method network 'iden3' with blockchain 'eth' and network 'main' already registered with another flag '100001'"
+    },
+    {
+      description: 'register new did method with existing method byte',
+      data: {
+        method: 'new_method',
+        blockchain: 'new_chain',
+        network: 'new_net',
+        networkFlag: 0b0001_0001,
+        chainId: 101,
+        methodByte: 0b00000001
+      },
+      err: "DID method byte '1' already registered"
+    },
+    {
+      description: 'register new did method with existing method byte',
+      data: {
+        method: 'new_method',
+        blockchain: Blockchain.Ethereum,
+        network: NetworkId.Main,
+        networkFlag: 0b0001_0001,
+        chainId: 101,
+        methodByte: 0b10000000
+      },
+      err: "chainId 'eth:main' already registered with value '1'"
+    },
+    {
+      description:
+        'register new network and chain with existing networkFlag for existing existing did method',
+      data: {
+        method: DidMethod.Iden3,
+        blockchain: 'supa_chain',
+        network: 'supa_net',
+        networkFlag: 0b00010000 | 0b00000001
+      },
+      err: 'DID network flag  undefined is already registered'
     }
   ];
   for (let i = 0; i < testCases.length; i++) {