diff --git a/landing/competitor-feature.react.js b/landing/competitor-feature.react.js
--- a/landing/competitor-feature.react.js
+++ b/landing/competitor-feature.react.js
@@ -13,8 +13,8 @@
 
 function useDescriptionContent(
   description: string | $ReadOnlyArray<string>,
-  descriptionClassName,
-  descriptionMultiClassName,
+  descriptionClassName: string,
+  descriptionMultiClassName: string,
 ) {
   return React.useMemo(() => {
     if (typeof description === 'string') {
diff --git a/landing/investor-profile.react.js b/landing/investor-profile.react.js
--- a/landing/investor-profile.react.js
+++ b/landing/investor-profile.react.js
@@ -49,7 +49,10 @@
     css.involvement,
   ]);
 
-  const stopPropagation = React.useCallback(e => e.stopPropagation(), []);
+  const stopPropagation = React.useCallback(
+    (e: SyntheticEvent<HTMLAnchorElement>) => e.stopPropagation(),
+    [],
+  );
 
   let websiteIcon;
   if (website) {
diff --git a/landing/keyserver-faq.react.js b/landing/keyserver-faq.react.js
--- a/landing/keyserver-faq.react.js
+++ b/landing/keyserver-faq.react.js
@@ -15,7 +15,7 @@
     css.questionText,
   ]);
 
-  const [activeFAQIndex, setActiveFAQIndex] = React.useState(null);
+  const [activeFAQIndex, setActiveFAQIndex] = React.useState<?number>(null);
 
   const onClickFAQItem = React.useCallback(
     (index: number) => {
diff --git a/landing/keyservers.react.js b/landing/keyservers.react.js
--- a/landing/keyservers.react.js
+++ b/landing/keyservers.react.js
@@ -51,7 +51,7 @@
     });
   }, []);
 
-  const [eyeNode, setEyeNode] = React.useState(null);
+  const [eyeNode, setEyeNode] = React.useState<?HTMLElement>(null);
   useIsomorphicLayoutEffect(() => {
     if (!eyeNode) {
       return undefined;
@@ -60,7 +60,7 @@
     return () => eyeNode.removeEventListener('load', onEyeIllustrationLoad);
   }, [eyeNode, onEyeIllustrationLoad]);
 
-  const [cloudNode, setCloudNode] = React.useState(null);
+  const [cloudNode, setCloudNode] = React.useState<?HTMLElement>(null);
   useIsomorphicLayoutEffect(() => {
     if (!cloudNode) {
       return undefined;
diff --git a/landing/subscription-form.react.js b/landing/subscription-form.react.js
--- a/landing/subscription-form.react.js
+++ b/landing/subscription-form.react.js
@@ -1,6 +1,7 @@
 // @flow
 
 import classNames from 'classnames';
+import invariant from 'invariant';
 import * as React from 'react';
 
 import { validEmailRegex } from 'lib/shared/account-utils.js';
@@ -83,9 +84,14 @@
   const buttonClassName = classNames([typography.paragraph2, btnStyle]);
   const errorTextClassName = classNames([typography.paragraph2, css.errorText]);
 
-  const onEmailChange = React.useCallback(e => {
-    setEmail(e.target.value);
-  }, []);
+  const onEmailChange = React.useCallback(
+    (e: SyntheticEvent<HTMLInputElement>) => {
+      const { target } = e;
+      invariant(target instanceof HTMLInputElement, 'target not input');
+      setEmail(target.value);
+    },
+    [],
+  );
 
   let errorText;
   if (subscriptionFormStatus.status === 'error') {