diff --git a/packages/types/src/interfaces/metadata/types.ts b/packages/types/src/interfaces/metadata/types.ts
index 09b083d147..1b6f8d06f2 100644
--- a/packages/types/src/interfaces/metadata/types.ts
+++ b/packages/types/src/interfaces/metadata/types.ts
@@ -132,7 +132,7 @@ export interface FunctionMetadataV14 extends Struct {
   readonly fields: Vec<SiField>;
   readonly index: u8;
   readonly docs: Vec<Text>;
-  readonly args: Vec<FunctionArgumentMetadataLatest>;
+  readonly args: Vec<FunctionArgumentMetadataV14>;
 }
 
 /** @name FunctionMetadataV9 */
diff --git a/packages/types/src/interfaces/metadata/v14.ts b/packages/types/src/interfaces/metadata/v14.ts
index b3cf4e507f..7154b232bf 100644
--- a/packages/types/src/interfaces/metadata/v14.ts
+++ b/packages/types/src/interfaces/metadata/v14.ts
@@ -28,7 +28,7 @@ export const v14: DefinitionsTypes = {
   FunctionArgumentMetadataV14: 'FunctionArgumentMetadataV13',
   FunctionMetadataV14: {
     ...SiVariant,
-    args: 'Vec<FunctionArgumentMetadataLatest>'
+    args: 'Vec<FunctionArgumentMetadataV14>'
   },
 
   // V14
diff --git a/packages/types/src/metadata/decorate/extrinsics/index.ts b/packages/types/src/metadata/decorate/extrinsics/index.ts
index b373abf4c5..095d5cd27a 100644
--- a/packages/types/src/metadata/decorate/extrinsics/index.ts
+++ b/packages/types/src/metadata/decorate/extrinsics/index.ts
@@ -7,6 +7,7 @@ import type { Extrinsics, ModuleExtrinsics } from '../types';
 
 import { stringCamelCase } from '@polkadot/util';
 
+import { getSiName } from '../../util';
 import { createUnchecked } from './createUnchecked';
 
 /** @internal */
@@ -25,7 +26,7 @@ export function decorateExtrinsics (registry: Registry, { lookup, pallets }: Met
             ...variant,
             args: variant.fields.map(({ name, type }, index) => ({
               name: stringCamelCase(name.unwrapOr(`param${index}`)),
-              type: lookup.getTypeDef(type).type
+              type: getSiName(lookup, type)
             }))
           });
 
diff --git a/packages/types/src/metadata/util/getSiName.ts b/packages/types/src/metadata/util/getSiName.ts
new file mode 100644
index 0000000000..e68caae6db
--- /dev/null
+++ b/packages/types/src/metadata/util/getSiName.ts
@@ -0,0 +1,10 @@
+// Copyright 2017-2021 @polkadot/types authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import type { PortableRegistry, SiLookupTypeId } from '../../interfaces';
+
+export function getSiName (lookup: PortableRegistry, type: SiLookupTypeId): string {
+  const typeDef = lookup.getTypeDef(type);
+
+  return typeDef.lookupName || typeDef.type;
+}
diff --git a/packages/types/src/metadata/util/index.ts b/packages/types/src/metadata/util/index.ts
index 1b2c3c08a0..9d2efcea27 100644
--- a/packages/types/src/metadata/util/index.ts
+++ b/packages/types/src/metadata/util/index.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 export { flattenUniq } from './flattenUniq';
+export { getSiName } from './getSiName';
 export { getUniqTypes } from './getUniqTypes';
 export { toCallsOnly } from './toCallsOnly';
 export { validateTypes } from './validateTypes';
diff --git a/packages/types/src/primitive/StorageKey.ts b/packages/types/src/primitive/StorageKey.ts
index 31855be2f2..0a3e14c7b4 100644
--- a/packages/types/src/primitive/StorageKey.ts
+++ b/packages/types/src/primitive/StorageKey.ts
@@ -9,6 +9,7 @@ import type { StorageEntry } from './types';
 
 import { assert, isFunction, isString, isU8a } from '@polkadot/util';
 
+import { getSiName } from '../metadata/util';
 import { Bytes } from './Bytes';
 
 interface Decoded {
@@ -42,8 +43,7 @@ export function unwrapStorageSi (type: StorageEntryTypeLatest): SiLookupTypeId {
 
 /** @internal */
 export function unwrapStorageType (registry: Registry, type: StorageEntryTypeLatest, isOptional?: boolean): keyof InterfaceTypes {
-  const typeDef = registry.lookup.getTypeDef(unwrapStorageSi(type));
-  const outputType = typeDef.lookupName || typeDef.type;
+  const outputType = getSiName(registry.lookup, unwrapStorageSi(type));
 
   return isOptional
     ? `Option<${outputType}>` as keyof InterfaceTypes