diff --git a/packages/ui-app/src/Call.tsx b/packages/ui-app/src/Call.tsx
index 731a92e504..e888d608dc 100644
--- a/packages/ui-app/src/Call.tsx
+++ b/packages/ui-app/src/Call.tsx
@@ -2,12 +2,12 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
-import { IExtrinsic, IMethod } from '@polkadot/types/types';
+import { Codec, IExtrinsic, IMethod } from '@polkadot/types/types';
 import { BareProps, I18nProps } from './types';
 
 import React from 'react';
 import styled from 'styled-components';
-import { Method, getTypeDef } from '@polkadot/types';
+import { Method, getTypeDef, TypeDef } from '@polkadot/types';
 import Params from '@polkadot/ui-params';
 
 import Static from './Static';
@@ -15,10 +15,10 @@ import { classes } from './util';
 import translate from './translate';
 
 export type Props = I18nProps & BareProps & {
-  children?: React.ReactNode,
-  value: IExtrinsic | IMethod,
-  withHash?: boolean,
-  mortality?: string
+  children?: React.ReactNode;
+  value: IExtrinsic | IMethod;
+  withHash?: boolean;
+  mortality?: string;
 };
 
 const Wrapper = styled.div`
@@ -33,11 +33,11 @@ const Wrapper = styled.div`
 class Call extends React.PureComponent<Props> {
   public render (): React.ReactNode {
     const { children, className, style, mortality, value, withHash, t } = this.props;
-    const params = Method.filterOrigin(value.meta).map(({ name, type }) => ({
+    const params = Method.filterOrigin(value.meta).map(({ name, type }): { name: string; type: TypeDef } => ({
       name: name.toString(),
       type: getTypeDef(type)
     }));
-    const values = value.args.map((value) => ({
+    const values = value.args.map((value): { isValid: boolean; value: Codec } => ({
       isValid: true,
       value
     }));
diff --git a/packages/ui-params/src/index.tsx b/packages/ui-params/src/index.tsx
index a594b19676..f6956a05c1 100644
--- a/packages/ui-params/src/index.tsx
+++ b/packages/ui-params/src/index.tsx
@@ -30,10 +30,10 @@ interface Props extends I18nProps {
 }
 
 interface State {
-  handlers: RawParamOnChange[];
+  handlers?: RawParamOnChange[];
   onChangeParam: (at: number, next: RawParamOnChangeValue) => void;
-  params: Param[];
-  values: RawParams;
+  params?: Param[];
+  values?: RawParams;
 }
 
 class Params extends React.PureComponent<Props, State> {
@@ -43,10 +43,7 @@ class Params extends React.PureComponent<Props, State> {
     super(props);
 
     this.state = {
-      handlers: [],
-      onChangeParam: this.onChangeParam,
-      params: [],
-      values: []
+      onChangeParam: this.onChangeParam
     };
   }
 
@@ -84,7 +81,7 @@ class Params extends React.PureComponent<Props, State> {
     const { values } = this.state;
 
     if (!isDisabled && prevState.values !== values) {
-      onChange && onChange(values);
+      onChange && onChange(values || []);
     }
   }
 
@@ -130,7 +127,7 @@ class Params extends React.PureComponent<Props, State> {
 
     this.setState(
       (prevState: State): State => ({
-        values: prevState.values.map((prev, index): RawParam =>
+        values: (prevState.values || []).map((prev, index): RawParam =>
           index !== at
             ? prev
             : {
@@ -147,7 +144,7 @@ class Params extends React.PureComponent<Props, State> {
     const { values } = this.state;
     const { onChange, isDisabled } = this.props;
 
-    if (isDisabled) {
+    if (isDisabled || !values) {
       return;
     }