diff --git a/IntegrationTests/LayoutEventsTest.js b/IntegrationTests/LayoutEventsTest.js
index 609d786fc8..46efb579d8 100644
--- a/IntegrationTests/LayoutEventsTest.js
+++ b/IntegrationTests/LayoutEventsTest.js
@@ -19,7 +19,7 @@ import type {ViewStyleProp} from 'react-native/Libraries/StyleSheet/StyleSheet';
 
 const deepDiffer = require('react-native/Libraries/Utilities/differ/deepDiffer');
 
-function debug(...args) {
+function debug(...args: Array<void | Layout | string>) {
   // console.log.apply(null, arguments);
 }
 
@@ -119,16 +119,19 @@ class LayoutEventsTest extends React.Component<Props, State> {
   }
 
   onViewLayout: (e: LayoutEvent) => void = (e: LayoutEvent) => {
+    // $FlowFixMe[incompatible-call]
     debug('received view layout event\n', e.nativeEvent);
     this.setState({viewLayout: e.nativeEvent.layout}, this.checkLayout);
   };
 
   onTextLayout: (e: LayoutEvent) => void = (e: LayoutEvent) => {
+    // $FlowFixMe[incompatible-call]
     debug('received text layout event\n', e.nativeEvent);
     this.setState({textLayout: e.nativeEvent.layout}, this.checkLayout);
   };
 
   onImageLayout: (e: LayoutEvent) => void = (e: LayoutEvent) => {
+    // $FlowFixMe[incompatible-call]
     debug('received image layout event\n', e.nativeEvent);
     this.setState({imageLayout: e.nativeEvent.layout}, this.checkLayout);
   };
diff --git a/Libraries/Animated/__tests__/bezier-test.js b/Libraries/Animated/__tests__/bezier-test.js
index 1a02d7ad62..48bfdef0f2 100644
--- a/Libraries/Animated/__tests__/bezier-test.js
+++ b/Libraries/Animated/__tests__/bezier-test.js
@@ -19,21 +19,26 @@
 
 const bezier = require('../bezier');
 
-const identity = function (x) {
+const identity = function (x: number) {
   return x;
 };
 
-function assertClose(a, b, precision = 3) {
+function assertClose(a: number, b: number, precision: number = 3) {
   expect(a).toBeCloseTo(b, precision);
 }
 
-function makeAssertCloseWithPrecision(precision) {
-  return function (a, b) {
+function makeAssertCloseWithPrecision(precision: number) {
+  return function (a: number, b: number) {
     assertClose(a, b, precision);
   };
 }
 
-function allEquals(be1, be2, samples, assertion) {
+function allEquals(
+  be1: (x: number) => number,
+  be2: (x: number) => number,
+  samples: number,
+  assertion: $FlowFixMe,
+) {
   if (!assertion) {
     assertion = assertClose;
   }
@@ -43,8 +48,8 @@ function allEquals(be1, be2, samples, assertion) {
   }
 }
 
-function repeat(n) {
-  return function (f) {
+function repeat(n: number) {
+  return function (f: () => void) {
     for (let i = 0; i < n; ++i) {
       f();
     }
@@ -99,7 +104,7 @@ describe('bezier', function () {
           d = Math.random();
         const easing = bezier(a, b, c, d);
         const projected = bezier(b, a, d, c);
-        const composed = function (x) {
+        const composed = function (x: number) {
           return projected(easing(x));
         };
         allEquals(identity, composed, 100, makeAssertCloseWithPrecision(2));
@@ -135,7 +140,7 @@ describe('bezier', function () {
           c = 1 - a,
           d = 1 - b;
         const easing = bezier(a, b, c, d);
-        const sym = function (x) {
+        const sym = function (x: number) {
           return 1 - easing(1 - x);
         };
         allEquals(easing, sym, 100, makeAssertCloseWithPrecision(2));
diff --git a/Libraries/Lists/FlatList.js b/Libraries/Lists/FlatList.js
index 8e810372bd..a56962691c 100644
--- a/Libraries/Lists/FlatList.js
+++ b/Libraries/Lists/FlatList.js
@@ -459,7 +459,7 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
   _listRef: ?React.ElementRef<typeof VirtualizedList>;
   _virtualizedListPairs: Array<ViewabilityConfigCallbackPair> = [];
 
-  _captureRef = ref => {
+  _captureRef = (ref: ?React.ElementRef<typeof VirtualizedList>) => {
     this._listRef = ref;
   };
 
@@ -596,7 +596,7 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
       ? 'ListItemComponent'
       : 'renderItem';
 
-    const renderer = (props): React.Node => {
+    const renderer = (props: RenderItemProps<ItemT>): React.Node => {
       if (ListItemComponent) {
         // $FlowFixMe[not-a-component] Component isn't valid
         // $FlowFixMe[incompatible-type-arg] Component isn't valid
@@ -625,6 +625,7 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
             <View style={StyleSheet.compose(styles.row, columnWrapperStyle)}>
               {item.map((it, kk) => {
                 const element = renderer({
+                  // $FlowFixMe[incompatible-call]
                   item: it,
                   index: index * cols + kk,
                   separators: info.separators,
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxData-test.js b/Libraries/LogBox/Data/__tests__/LogBoxData-test.js
index 0856f95101..7b135b8d87 100644
--- a/Libraries/LogBox/Data/__tests__/LogBoxData-test.js
+++ b/Libraries/LogBox/Data/__tests__/LogBoxData-test.js
@@ -51,7 +51,7 @@ const observe = () => {
   };
 };
 
-const addLogs = (logs, options) => {
+const addLogs = (logs: Array<string>, options: void | {flush: boolean}) => {
   logs.forEach(message => {
     LogBoxData.addLog({
       level: 'warn',
@@ -68,7 +68,10 @@ const addLogs = (logs, options) => {
   });
 };
 
-const addSoftErrors = (errors, options) => {
+const addSoftErrors = (
+  errors: Array<string>,
+  options: void | {flush: boolean},
+) => {
   errors.forEach(error => {
     LogBoxData.addException({
       message: '',
@@ -89,7 +92,10 @@ const addSoftErrors = (errors, options) => {
   });
 };
 
-const addFatalErrors = (errors, options) => {
+const addFatalErrors = (
+  errors: Array<$FlowFixMe>,
+  options: void | {flush: boolean},
+) => {
   errors.forEach(error => {
     LogBoxData.addException({
       message: '',
@@ -112,7 +118,7 @@ const addFatalErrors = (errors, options) => {
   });
 };
 
-const addSyntaxError = options => {
+const addSyntaxError = (options: $FlowFixMe) => {
   addFatalErrors(
     [
       {
diff --git a/Libraries/LogBox/UI/__tests__/LogBoxInspectorStackFrames-test.js b/Libraries/LogBox/UI/__tests__/LogBoxInspectorStackFrames-test.js
index d9ff74d835..8e247e699d 100644
--- a/Libraries/LogBox/UI/__tests__/LogBoxInspectorStackFrames-test.js
+++ b/Libraries/LogBox/UI/__tests__/LogBoxInspectorStackFrames-test.js
@@ -18,7 +18,7 @@ const {} = require('../LogBoxInspectorStackFrames');
 const LogBoxLog = require('../../Data/LogBoxLog').default;
 const render = require('../../../../jest/renderer');
 
-const createLogWithFrames = collapsedOptions => {
+const createLogWithFrames = (collapsedOptions: Array<?boolean>) => {
   return new LogBoxLog({
     level: 'warn',
     isComponentError: false,
@@ -32,7 +32,7 @@ const createLogWithFrames = collapsedOptions => {
   });
 };
 
-const createCollapsedFrames = collapsedOptions => {
+const createCollapsedFrames = (collapsedOptions: Array<?boolean>) => {
   return collapsedOptions.map(option => ({
     column: 1,
     file: 'dependency.js',
diff --git a/Libraries/LogBox/__tests__/LogBox-test.js b/Libraries/LogBox/__tests__/LogBox-test.js
index bc793a56b2..d86bd3b12b 100644
--- a/Libraries/LogBox/__tests__/LogBox-test.js
+++ b/Libraries/LogBox/__tests__/LogBox-test.js
@@ -16,7 +16,7 @@ const LogBoxData = require('../Data/LogBoxData');
 
 declare var console: any;
 
-function mockFilterResult(returnValues) {
+function mockFilterResult(returnValues: $FlowFixMe) {
   (LogBoxData.checkWarningFilter: any).mockReturnValue({
     finalFormat: 'Warning: ...',
     forceDialogImmediately: false,
diff --git a/packages/react-native-codegen/src/parsers/flow/components/events.js b/packages/react-native-codegen/src/parsers/flow/components/events.js
index acb98d0c88..b6a3db01f5 100644
--- a/packages/react-native-codegen/src/parsers/flow/components/events.js
+++ b/packages/react-native-codegen/src/parsers/flow/components/events.js
@@ -18,8 +18,8 @@ import type {
 
 function getPropertyType(
   name,
-  optional,
-  typeAnnotation,
+  optional: boolean,
+  typeAnnotation: $FlowFixMe,
 ): NamedShape<EventTypeAnnotation> {
   const type =
     typeAnnotation.type === 'GenericTypeAnnotation'
@@ -98,10 +98,10 @@ function getPropertyType(
 }
 
 function findEventArgumentsAndType(
-  typeAnnotation,
-  types,
-  bubblingType,
-  paperName,
+  typeAnnotation: $FlowFixMe,
+  types: TypeMap,
+  bubblingType: void | 'direct' | 'bubble',
+  paperName: ?$FlowFixMe,
 ) {
   if (!typeAnnotation.id) {
     throw new Error("typeAnnotation of event doesn't have a name");
@@ -163,7 +163,7 @@ function buildPropertiesForEvent(property): NamedShape<EventTypeAnnotation> {
   return getPropertyType(name, optional, typeAnnotation);
 }
 
-function getEventArgument(argumentProps, name) {
+function getEventArgument(argumentProps, name: $FlowFixMe) {
   return {
     type: 'ObjectTypeAnnotation',
     properties: argumentProps.map(buildPropertiesForEvent),
diff --git a/packages/react-native-codegen/src/parsers/typescript/components/events.js b/packages/react-native-codegen/src/parsers/typescript/components/events.js
index e5c1fa6872..cd94fa0059 100644
--- a/packages/react-native-codegen/src/parsers/typescript/components/events.js
+++ b/packages/react-native-codegen/src/parsers/typescript/components/events.js
@@ -18,7 +18,7 @@ import type {
 
 function getPropertyType(
   name,
-  optional,
+  optional: boolean,
   typeAnnotation,
 ): NamedShape<EventTypeAnnotation> {
   const type =
@@ -118,10 +118,10 @@ function getPropertyType(
 }
 
 function findEventArgumentsAndType(
-  typeAnnotation,
-  types,
-  bubblingType,
-  paperName,
+  typeAnnotation: $FlowFixMe,
+  types: TypeMap,
+  bubblingType: void | 'direct' | 'bubble',
+  paperName: ?$FlowFixMe,
 ) {
   if (!typeAnnotation.typeName) {
     throw new Error("typeAnnotation of event doesn't have a name");
@@ -177,7 +177,7 @@ function buildPropertiesForEvent(property): NamedShape<EventTypeAnnotation> {
   return getPropertyType(name, optional, typeAnnotation);
 }
 
-function getEventArgument(argumentProps, name) {
+function getEventArgument(argumentProps, name: $FlowFixMe) {
   return {
     type: 'ObjectTypeAnnotation',
     properties: argumentProps.map(buildPropertiesForEvent),
diff --git a/packages/rn-tester/js/examples/Accessibility/AccessibilityExample.js b/packages/rn-tester/js/examples/Accessibility/AccessibilityExample.js
index ce8151ce8f..fb917d19dc 100644
--- a/packages/rn-tester/js/examples/Accessibility/AccessibilityExample.js
+++ b/packages/rn-tester/js/examples/Accessibility/AccessibilityExample.js
@@ -1148,10 +1148,19 @@ class DisplayOptionsStatusExample extends React.Component<{}> {
   }
 }
 
-function DisplayOptionStatusExample({optionName, optionChecker, notification}) {
+function DisplayOptionStatusExample({
+  optionName,
+  optionChecker,
+  notification,
+}: {
+  notification: string,
+  optionChecker: () => Promise<boolean>,
+  optionName: string,
+}) {
   const [statusEnabled, setStatusEnabled] = React.useState(false);
   React.useEffect(() => {
     const listener = AccessibilityInfo.addEventListener(
+      // $FlowFixMe[prop-missing]
       notification,
       setStatusEnabled,
     );
diff --git a/packages/rn-tester/js/examples/Appearance/AppearanceExample.js b/packages/rn-tester/js/examples/Appearance/AppearanceExample.js
index d19d8a5832..601bcdf7fb 100644
--- a/packages/rn-tester/js/examples/Appearance/AppearanceExample.js
+++ b/packages/rn-tester/js/examples/Appearance/AppearanceExample.js
@@ -52,7 +52,7 @@ class ColorSchemeSubscription extends React.Component<
   }
 }
 
-const ThemedContainer = props => (
+const ThemedContainer = (props: {children: React.Node}) => (
   <RNTesterThemeContext.Consumer>
     {theme => {
       return (
@@ -69,7 +69,7 @@ const ThemedContainer = props => (
   </RNTesterThemeContext.Consumer>
 );
 
-const ThemedText = props => (
+const ThemedText = (props: {children: React.Node}) => (
   <RNTesterThemeContext.Consumer>
     {theme => {
       return <Text style={{color: theme.LabelColor}}>{props.children}</Text>;
@@ -89,7 +89,7 @@ const AppearanceViaHook = () => {
   );
 };
 
-const ColorShowcase = props => (
+const ColorShowcase = (props: {themeName: string}) => (
   <RNTesterThemeContext.Consumer>
     {theme => {
       return (