diff --git a/packages/ui-params/src/Param/Tuple.tsx b/packages/ui-params/src/Param/Tuple.tsx
index 53349e6d60..0d931774b2 100644
--- a/packages/ui-params/src/Param/Tuple.tsx
+++ b/packages/ui-params/src/Param/Tuple.tsx
@@ -91,7 +91,7 @@ export default class Tuple extends React.PureComponent<Props, State> {
           const { onChange } = this.props;
 
           onChange && onChange({
-            isValid: values.reduce((result, { isValid }) => result && isValid, true),
+            isValid: values.reduce((result: boolean, { isValid }) => result && isValid, true),
             value: values.map(({ value }) => value)
           });
         }
diff --git a/packages/ui-params/src/Param/Vector.tsx b/packages/ui-params/src/Param/Vector.tsx
index a5e9f04089..78418556d7 100644
--- a/packages/ui-params/src/Param/Vector.tsx
+++ b/packages/ui-params/src/Param/Vector.tsx
@@ -121,7 +121,7 @@ class Vector extends React.PureComponent<Props, State> {
           const { onChange } = this.props;
 
           onChange && onChange({
-            isValid: values.reduce((result, { isValid }) => result && isValid, true),
+            isValid: values.reduce((result: boolean, { isValid }) => result && isValid, true),
             value: values.map(({ value }) => value)
           });
         }