diff --git a/packages/api/src/augment/rpc.ts b/packages/api/src/augment/rpc.ts
index a3b80d3738..881a203911 100644
--- a/packages/api/src/augment/rpc.ts
+++ b/packages/api/src/augment/rpc.ts
@@ -144,11 +144,11 @@ declare module '@polkadot/rpc-core/types.jsonrpc' {
       /**
        * Get offchain local storage under given key and prefix
        **/
-      localStorageGet: AugmentedRpc<(kind: StorageKind | ('__UNUSED' | 'PERSISTENT' | 'LOCAL') | number | Uint8Array, key: Bytes | string | Uint8Array) => Observable<Option<Bytes>>>;
+      localStorageGet: AugmentedRpc<(kind: StorageKind | '__UNUSED' | 'PERSISTENT' | 'LOCAL' | number | Uint8Array, key: Bytes | string | Uint8Array) => Observable<Option<Bytes>>>;
       /**
        * Set offchain local storage under given key and prefix
        **/
-      localStorageSet: AugmentedRpc<(kind: StorageKind | ('__UNUSED' | 'PERSISTENT' | 'LOCAL') | number | Uint8Array, key: Bytes | string | Uint8Array, value: Bytes | string | Uint8Array) => Observable<Null>>;
+      localStorageSet: AugmentedRpc<(kind: StorageKind | '__UNUSED' | 'PERSISTENT' | 'LOCAL' | number | Uint8Array, key: Bytes | string | Uint8Array, value: Bytes | string | Uint8Array) => Observable<Null>>;
     };
     payment: {
       /**
diff --git a/packages/api/src/augment/tx.ts b/packages/api/src/augment/tx.ts
index 356e28fa5f..4ad7e2af95 100644
--- a/packages/api/src/augment/tx.ts
+++ b/packages/api/src/augment/tx.ts
@@ -237,7 +237,7 @@ declare module '@polkadot/api/types/submittable' {
        * # <weight>
        * # </weight>
        **/
-      delegate: AugmentedSubmittable<(to: AccountId | string | Uint8Array, conviction: Conviction | ('None' | 'Locked1x' | 'Locked2x' | 'Locked3x' | 'Locked4x' | 'Locked5x' | 'Locked6x') | number | Uint8Array, balance: BalanceOf | AnyNumber | Uint8Array) => SubmittableExtrinsic<ApiType>>;
+      delegate: AugmentedSubmittable<(to: AccountId | string | Uint8Array, conviction: Conviction | 'None'|'Locked1x'|'Locked2x'|'Locked3x'|'Locked4x'|'Locked5x'|'Locked6x' | number | Uint8Array, balance: BalanceOf | AnyNumber | Uint8Array) => SubmittableExtrinsic<ApiType>>;
       /**
        * Schedule an emergency cancellation of a referendum. Cannot happen twice to the same
        * referendum.
@@ -375,7 +375,7 @@ declare module '@polkadot/api/types/submittable' {
        * # <weight>
        * # </weight>
        **/
-      proxyDelegate: AugmentedSubmittable<(to: AccountId | string | Uint8Array, conviction: Conviction | ('None' | 'Locked1x' | 'Locked2x' | 'Locked3x' | 'Locked4x' | 'Locked5x' | 'Locked6x') | number | Uint8Array, balance: BalanceOf | AnyNumber | Uint8Array) => SubmittableExtrinsic<ApiType>>;
+      proxyDelegate: AugmentedSubmittable<(to: AccountId | string | Uint8Array, conviction: Conviction | 'None'|'Locked1x'|'Locked2x'|'Locked3x'|'Locked4x'|'Locked5x'|'Locked6x' | number | Uint8Array, balance: BalanceOf | AnyNumber | Uint8Array) => SubmittableExtrinsic<ApiType>>;
       /**
        * Remove a proxied vote for a referendum.
        * Exactly equivalent to `remove_vote` except that it operates on the account that the
@@ -1144,7 +1144,7 @@ declare module '@polkadot/api/types/submittable' {
        * Total Complexity: O(M + logM + B + X)
        * # </weight>
        **/
-      judgeSuspendedCandidate: AugmentedSubmittable<(who: AccountId | string | Uint8Array, judgement: SocietyJudgement | ('Rebid' | 'Reject' | 'Approve') | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
+      judgeSuspendedCandidate: AugmentedSubmittable<(who: AccountId | string | Uint8Array, judgement: SocietyJudgement | 'Rebid'|'Reject'|'Approve' | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
       /**
        * Allow suspension judgement origin to make judgement on a suspended member.
        * If a suspended member is forgiven, we simply add them back as a member, not affecting
@@ -1322,7 +1322,7 @@ declare module '@polkadot/api/types/submittable' {
        * unless the `origin` falls below _existential deposit_ and gets removed as dust.
        * # </weight>
        **/
-      bond: AugmentedSubmittable<(controller: LookupSource | Address | AccountId | AccountIndex | string | Uint8Array, value: Compact<BalanceOf> | AnyNumber | Uint8Array, payee: RewardDestination | ('Staked' | 'Stash' | 'Controller') | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
+      bond: AugmentedSubmittable<(controller: LookupSource | Address | AccountId | AccountIndex | string | Uint8Array, value: Compact<BalanceOf> | AnyNumber | Uint8Array, payee: RewardDestination | 'Staked'|'Stash'|'Controller' | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
       /**
        * Add some extra amount that have appeared in the stash `free_balance` into the balance up
        * for staking.
@@ -1506,7 +1506,7 @@ declare module '@polkadot/api/types/submittable' {
        * - Writes are limited to the `origin` account key.
        * # </weight>
        **/
-      setPayee: AugmentedSubmittable<(payee: RewardDestination | ('Staked' | 'Stash' | 'Controller') | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
+      setPayee: AugmentedSubmittable<(payee: RewardDestination | 'Staked'|'Stash'|'Controller' | number | Uint8Array) => SubmittableExtrinsic<ApiType>>;
       /**
        * The ideal number of validators.
        **/
diff --git a/packages/typegen/src/generate/interfaceRegistry.ts b/packages/typegen/src/generate/interfaceRegistry.ts
index 6e0fc1259c..5383fa18b1 100644
--- a/packages/typegen/src/generate/interfaceRegistry.ts
+++ b/packages/typegen/src/generate/interfaceRegistry.ts
@@ -20,6 +20,7 @@ export function generateInterfaceTypes (importDefinitions: { [importPath: string
 
     const imports = createImports(importDefinitions);
     const definitions = imports.definitions;
+
     const primitives = Object
       .keys(primitiveClasses)
       .filter((name): boolean => !!name.indexOf('Generic'))
@@ -32,13 +33,19 @@ export function generateInterfaceTypes (importDefinitions: { [importPath: string
         ].join('\n');
       }, '');
 
+    const existingTypes: Record<string, boolean> = {};
+
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     const srml = Object.entries(definitions).reduce((accumulator, [_defName, { types }]): string => {
       setImports(definitions, imports, Object.keys(types));
 
+      const uniqueTypes = Object.keys(types).filter((type) => !existingTypes[type]);
+
+      uniqueTypes.forEach((type) => { existingTypes[type] = true; });
+
       return [
         accumulator,
-        ...Object.keys(types).map((type): string =>
+        ...uniqueTypes.map((type): string =>
           getDerivedTypes(definitions, type, types[type], imports).map(indent(4)).join('\n')
         )
       ].join('\n');
diff --git a/packages/typegen/src/util/derived.ts b/packages/typegen/src/util/derived.ts
index 73599c0483..11655b97f2 100644
--- a/packages/typegen/src/util/derived.ts
+++ b/packages/typegen/src/util/derived.ts
@@ -27,7 +27,7 @@ import { formatType } from './formatting';
 import { setImports, TypeImports } from './imports';
 
 function arrayToStrType (arr: string[]): string {
-  return `(${arr.map((c): string => `'${c}'`).join(' | ')})`;
+  return `${arr.map((c): string => `'${c}'`).join(' | ')}`;
 }
 
 const voteConvictions = arrayToStrType(AllConvictions);