diff --git a/Libraries/Utilities/BackHandler.android.js b/Libraries/Utilities/BackHandler.android.js
index e6e3d035295860..ed5bb00d96abf3 100644
--- a/Libraries/Utilities/BackHandler.android.js
+++ b/Libraries/Utilities/BackHandler.android.js
@@ -63,11 +63,11 @@ type TBackHandler = {|
   +exitApp: () => void,
   +addEventListener: (
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ) => {remove: () => void, ...},
   +removeEventListener: (
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ) => void,
 |};
 const BackHandler: TBackHandler = {
@@ -87,7 +87,7 @@ const BackHandler: TBackHandler = {
    */
   addEventListener: function(
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ): {remove: () => void, ...} {
     if (_backPressSubscriptions.indexOf(handler) === -1) {
       _backPressSubscriptions.push(handler);
@@ -102,7 +102,7 @@ const BackHandler: TBackHandler = {
    */
   removeEventListener: function(
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ): void {
     if (_backPressSubscriptions.indexOf(handler) !== -1) {
       _backPressSubscriptions.splice(
diff --git a/Libraries/Utilities/BackHandler.ios.js b/Libraries/Utilities/BackHandler.ios.js
index ff2f1c862e548f..f7ed0515f2d485 100644
--- a/Libraries/Utilities/BackHandler.ios.js
+++ b/Libraries/Utilities/BackHandler.ios.js
@@ -54,11 +54,11 @@ type TBackHandler = {|
   +exitApp: () => void,
   +addEventListener: (
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ) => {remove: () => void, ...},
   +removeEventListener: (
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ) => void,
 |};
 
@@ -93,7 +93,7 @@ if (Platform.isTV) {
 
     addEventListener: function(
       eventName: BackPressEventName,
-      handler: Function,
+      handler: () => ?boolean,
     ): {remove: () => void, ...} {
       _backPressSubscriptions.add(handler);
       return {
@@ -103,7 +103,7 @@ if (Platform.isTV) {
 
     removeEventListener: function(
       eventName: BackPressEventName,
-      handler: Function,
+      handler: () => ?boolean,
     ): void {
       _backPressSubscriptions.delete(handler);
     },
diff --git a/Libraries/Utilities/__mocks__/BackHandler.js b/Libraries/Utilities/__mocks__/BackHandler.js
index 8422b05057c6e5..b90bf09d870fba 100644
--- a/Libraries/Utilities/__mocks__/BackHandler.js
+++ b/Libraries/Utilities/__mocks__/BackHandler.js
@@ -16,7 +16,7 @@ const BackHandler = {
 
   addEventListener: function(
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ): {remove: () => void} {
     _backPressSubscriptions.add(handler);
     return {
@@ -26,7 +26,7 @@ const BackHandler = {
 
   removeEventListener: function(
     eventName: BackPressEventName,
-    handler: Function,
+    handler: () => ?boolean,
   ): void {
     _backPressSubscriptions.delete(handler);
   },